Fix reset to BL3-1 instructions in user guide
Fix reset to BL3-1 instructions in user guide

Fix the instructions for resetting to the BL3-1 entrypoint in the
user guide. The BL3-1 and BL3-2 image locations changed in the fix
to ARM-software/tf-issues#117 (commit a1b6db6).

Fixes ARM-software/tf-issues#237

Change-Id: I764eb17c66034511efb984c0e7cfda29bd99198f

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