Merge branch 'master' of https://source.denx.de/u-boot/custodians/u-boot-sh

Add empty weak assembler function armv8_switch_to_el2_prep() which is
jumped to just before U-Boot determines which EL it is running in and
decides which path to take to boot the Linux kernel. Add
IH_TYPE_TFA_BL31 into supported images type, to allow implementation of
board specific U_BOOT_FIT_LOADABLE_HANDLER(IH_TYPE_TFA_BL31, ...) TFA
BL31 loadable handler for fitImages.

This PR contains common hooks which are noop, R-Car Gen4 board specific
implementation using these hooks is coming in next PR.