To support booting the kernel in EL2 some of the EL0 and EL1 registers
are changed to point to an EL2 version. To get access to the EL0/EL1
version of these registers we need to use the new EL02 and EL12
registers, e.g. to access elr_el1 from the host we would use elr_el12.
Add macros that can be different on VHE vs non-VHE code so these
registers can be accessed in the correct way.
Sponsored by: Arm Ltd