rockchip/rk3399: improve gpio driver and support get pull mode function
rockchip/rk3399: improve gpio driver and support get pull mode function

We may need gpio pull mode later, so add this function.
Besides fix a set pull mode bug, and save gpio clock gate,
when operate the gpio, we will enable gpio clock, when
finish gpio operate, restore gpio clock gate status.

Change-Id: Ia1d602804f571a17f5ddc499908663b968b02974

sbranden/arm-trusted-firmware,lsigithub/arm-trusted-firmware_public,lsigithub/arm-trusted-firmware_public,sbranden/arm-trusted-firmware,achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware