HAL: Rename platform reset function

Align with HAL design document:
 - Rename 'tfm_spm_hal_system_reset' to 'tfm_hal_system_reset'.
 - Create 'tfm_hal_platform.h' for HAL APIs.

Change-Id: Ic9cc92350aac41ee80a4e474425cdfe23795b69e
Signed-off-by: Summer Qin <summer.qin@arm.com>
diff --git a/platform/ext/common/tfm_platform.c b/platform/ext/common/tfm_platform.c
index 5e5ffed..fc9ecb7 100644
--- a/platform/ext/common/tfm_platform.c
+++ b/platform/ext/common/tfm_platform.c
@@ -27,7 +27,7 @@
     return TFM_PLAT_ERR_SUCCESS;
 }
 
-__WEAK void tfm_spm_hal_system_reset(void)
+__WEAK void tfm_hal_system_reset(void)
 {
     NVIC_SystemReset();
 }