FVP: Ensure system reset wake-up results in cold boot
FVP: Ensure system reset wake-up results in cold boot

platform_get_entrypoint() did not consider that a wakeup due to
System Reset Pin (by reading the power controller's PSYSR) requires
a cold boot. As a result, the code would execute the warm boot path
and eventually panic because entrypoint mailboxes are empty.

This patch ensures that the following wake-up reasons result in cold
boot:
  - Cold Power-on
  - System Reset Pin (includes reset by software)

Fixes ARM-software/tf-issues#217

Change-Id: I65ae0a0f7a46548b575900a5aac107d352b0e2cd

sandrine-bailleux/arm-trusted-firmware,idl3r/arm-trusted-firmware,lsigithub/arm-trusted-firmware_public,robixnai/arm-trusted-firmware,96boards/arm-trusted-firmware,jcastillo-arm/arm-trusted-firmware,jforissier/arm-trusted-firmware,ljerry/arm-trusted-firmware,longsleep/arm-trusted-firmware-pine64,longsleep/arm-trusted-firmware-pine64,yatharth-arm/arm-trusted-firmware,jforissier/arm-trusted-firmware,lsigithub/arm-trusted-firmware_public,mtk09422/arm-trusted-firmware,davwan01/arm-trusted-firmware,athoelke/arm-trusted-firmware,achingupta/arm-trusted-firmware,idl3r/arm-trusted-firmware,sbranden/arm-trusted-firmware,hzhuang1/arm-trusted-firmware,sandrine-bailleux-arm/arm-trusted-firmware,jcastillo-arm/arm-trusted-firmware,ljerry/arm-trusted-firmware,hzhuang1/arm-trusted-firmware,robixnai/arm-trusted-firmware,Leo-Yan/arm-trusted-firmware,athoelke/arm-trusted-firmware,96boards/arm-trusted-firmware,sandrine-bailleux-arm/arm-trusted-firmware,achingupta/arm-trusted-firmware,davwan01/arm-trusted-firmware,yatharth-arm/arm-trusted-firmware,sbranden/arm-trusted-firmware,vchong/arm-trusted-firmware,mtk09422/arm-trusted-firmware,sandrine-bailleux/arm-trusted-firmware,Leo-Yan/arm-trusted-firmware,vchong/arm-trusted-firmware