fs: Kconfig: Clean up representation of mutually exclusive options
fs: Kconfig: Clean up representation of mutually exclusive options

The flash and RAM disk options are mutually exclusive (evident e.g. in
both defining FS_VOLUME_SIZE and FS_BLOCK_SIZE variables), so they
should really be inside a choice-endchoice block. The duplicated
options can also taken care of with a single definition using
conditional default values.

Change-Id: I87733f0c342166a9e03aa0e1f34390d91107b137
Signed-off-by: Johan Hedberg <628991c7b0a19c384f9b99c21ec330ce952bb838@intel.com>

fbsder/zephyr,ldts/zephyr,mbolivar/zephyr,runchip/zephyr-cc3200,Vudentz/zephyr,mbolivar/zephyr,rsalveti/zephyr,nashif/zephyr,finikorg/zephyr,ldts/zephyr,Vudentz/zephyr,holtmann/zephyr,galak/zephyr,kraj/zephyr,punitvara/zephyr,holtmann/zephyr,bboozzoo/zephyr,pklazy/zephyr,erwango/zephyr,aceofall/zephyr-iotos,galak/zephyr,kraj/zephyr,bboozzoo/zephyr,tidyjiang8/zephyr-doc,sharronliu/zephyr,runchip/zephyr-cc3200,runchip/zephyr-cc3220,fractalclone/zephyr-riscv,Vudentz/zephyr,aceofall/zephyr-iotos,ldts/zephyr,punitvara/zephyr,tidyjiang8/zephyr-doc,Vudentz/zephyr,sharronliu/zephyr,zephyriot/zephyr,rsalveti/zephyr,finikorg/zephyr,nashif/zephyr,ldts/zephyr,punitvara/zephyr,tidyjiang8/zephyr-doc,aceofall/zephyr-iotos,GiulianoFranchetto/zephyr,bigdinotech/zephyr,fbsder/zephyr,sharronliu/zephyr,erwango/zephyr,zephyrproject-rtos/zephyr,erwango/zephyr,explora26/zephyr,galak/zephyr,bboozzoo/zephyr,rsalveti/zephyr,holtmann/zephyr,kraj/zephyr,runchip/zephyr-cc3200,Vudentz/zephyr,punitvara/zephyr,rsalveti/zephyr,zephyrproject-rtos/zephyr,runchip/zephyr-cc3220,bigdinotech/zephyr,mbolivar/zephyr,ldts/zephyr,explora26/zephyr,fbsder/zephyr,bigdinotech/zephyr,aceofall/zephyr-iotos,runchip/zephyr-cc3220,fractalclone/zephyr-riscv,erwango/zephyr,kraj/zephyr,sharronliu/zephyr,zephyriot/zephyr,GiulianoFranchetto/zephyr,holtmann/zephyr,fbsder/zephyr,runchip/zephyr-cc3220,galak/zephyr,Vudentz/zephyr,kraj/zephyr,pklazy/zephyr,fractalclone/zephyr-riscv,zephyriot/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,tidyjiang8/zephyr-doc,holtmann/zephyr,bboozzoo/zephyr,galak/zephyr,runchip/zephyr-cc3200,pklazy/zephyr,pklazy/zephyr,fractalclone/zephyr-riscv,explora26/zephyr,bigdinotech/zephyr,mbolivar/zephyr,aceofall/zephyr-iotos,nashif/zephyr,fbsder/zephyr,finikorg/zephyr,finikorg/zephyr,tidyjiang8/zephyr-doc,zephyriot/zephyr,GiulianoFranchetto/zephyr,erwango/zephyr,bboozzoo/zephyr,zephyriot/zephyr,sharronliu/zephyr,explora26/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,runchip/zephyr-cc3220,pklazy/zephyr,rsalveti/zephyr,nashif/zephyr,bigdinotech/zephyr,explora26/zephyr,fractalclone/zephyr-riscv,runchip/zephyr-cc3200,nashif/zephyr,GiulianoFranchetto/zephyr,mbolivar/zephyr