spi: change inline functions to static inline
spi: change inline functions to static inline

When compiling with optimization level 0 (-O0), the linker complains
about missing references to uart functions. This is due to compiler
treating this functions as extern, since -O0 disables function inlining,
as described in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49653

So change the declaration to static inline.

Change-Id: I2b75e686961878f299bb951b5a420f9738594795
Signed-off-by: Daniel Leung <d94e04d205b5962d7873a139ef298b03c1717f72@intel.com>

bboozzoo/zephyr,Vudentz/zephyr,fractalclone/zephyr-riscv,galak/zephyr,mbolivar/zephyr,coldnew/zephyr-project-fork,runchip/zephyr-cc3200,fractalclone/zephyr-riscv,sharronliu/zephyr,mirzak/zephyr-os,ldts/zephyr,aceofall/zephyr-iotos,punitvara/zephyr,jamesonwilliams/zephyr-kernel,erwango/zephyr,GiulianoFranchetto/zephyr,fbsder/zephyr,aceofall/zephyr-iotos,tidyjiang8/zephyr-doc,galak/zephyr,bboozzoo/zephyr,zephyriot/zephyr,runchip/zephyr-cc3220,coldnew/zephyr-project-fork,aceofall/zephyr-iotos,bigdinotech/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,kraj/zephyr,pklazy/zephyr,erwango/zephyr,GiulianoFranchetto/zephyr,mirzak/zephyr-os,runchip/zephyr-cc3220,fractalclone/zephyr-riscv,runchip/zephyr-cc3200,nashif/zephyr,tidyjiang8/zephyr-doc,zephyriot/zephyr,zephyrproject-rtos/zephyr,holtmann/zephyr,mbolivar/zephyr,sharronliu/zephyr,bigdinotech/zephyr,bigdinotech/zephyr,holtmann/zephyr,aceofall/zephyr-iotos,explora26/zephyr,pklazy/zephyr,bigdinotech/zephyr,explora26/zephyr,mirzak/zephyr-os,32bitmicro/zephyr,holtmann/zephyr,ldts/zephyr,bboozzoo/zephyr,mirzak/zephyr-os,punitvara/zephyr,holtmann/zephyr,zephyriot/zephyr,holtmann/zephyr,mirzak/zephyr-os,pklazy/zephyr,punitvara/zephyr,rsalveti/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,bboozzoo/zephyr,coldnew/zephyr-project-fork,erwango/zephyr,fbsder/zephyr,sharronliu/zephyr,jamesonwilliams/zephyr-kernel,kraj/zephyr,GiulianoFranchetto/zephyr,zephyrproject-rtos/zephyr,fbsder/zephyr,galak/zephyr,explora26/zephyr,coldnew/zephyr-project-fork,rsalveti/zephyr,jamesonwilliams/zephyr-kernel,jamesonwilliams/zephyr-kernel,finikorg/zephyr,tidyjiang8/zephyr-doc,finikorg/zephyr,sharronliu/zephyr,ldts/zephyr,runchip/zephyr-cc3220,zephyrproject-rtos/zephyr,aceofall/zephyr-iotos,bigdinotech/zephyr,galak/zephyr,Vudentz/zephyr,runchip/zephyr-cc3220,runchip/zephyr-cc3200,nashif/zephyr,32bitmicro/zephyr,32bitmicro/zephyr,Vudentz/zephyr,pklazy/zephyr,sharronliu/zephyr,Vudentz/zephyr,punitvara/zephyr,mbolivar/zephyr,zephyriot/zephyr,nashif/zephyr,runchip/zephyr-cc3200,GiulianoFranchetto/zephyr,finikorg/zephyr,zephyriot/zephyr,tidyjiang8/zephyr-doc,fbsder/zephyr,mbolivar/zephyr,runchip/zephyr-cc3220,tidyjiang8/zephyr-doc,nashif/zephyr,kraj/zephyr,rsalveti/zephyr,explora26/zephyr,fractalclone/zephyr-riscv,galak/zephyr,Vudentz/zephyr,erwango/zephyr,runchip/zephyr-cc3200,32bitmicro/zephyr,punitvara/zephyr,fractalclone/zephyr-riscv,rsalveti/zephyr,fbsder/zephyr,kraj/zephyr,Vudentz/zephyr,pklazy/zephyr,jamesonwilliams/zephyr-kernel,kraj/zephyr,ldts/zephyr,bboozzoo/zephyr,32bitmicro/zephyr,mbolivar/zephyr,finikorg/zephyr,coldnew/zephyr-project-fork,GiulianoFranchetto/zephyr,finikorg/zephyr,rsalveti/zephyr,erwango/zephyr,ldts/zephyr