HAL: Rename platform init function

Align with HAL design document:
 - Rename 'tfm_spm_hal_post_init' to 'tfm_hal_platform_init'.
 - Set 'tfm_hal_platform_init' to weak, and platform with specific init
   operation needs to override it.
 - Remove 'tfm_spm_hal_post_init_platform' and move the operations to
   'tfm_hal_platform_init'.

Change-Id: Ia96b3a6bae716d154edab8709eb6e277bafcb45e
Signed-off-by: Summer Qin <summer.qin@arm.com>
7 files changed