Set correct value for SYS_ID_REV_SHIFT in FVP
Set correct value for SYS_ID_REV_SHIFT in FVP

According to documentation, the Rev field is located at bit 28 in
the V2M sysid register.

Fixes ARM-software/tf-issues#179

Change-Id: I2abb7bdc092ccd3f41f8962dc8d8d8e44e8dfdc3

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