arm: Add support for HYP mode and LPAE page tables

arm: Add support for HYP mode and LPAE page tables

We currently always modify the SVC versions of registers and only support
the short descriptor PTE format.

Some boards however (like the RPi2) run in HYP mode. There, we need to modify
the HYP version of system registers and HYP mode only supports the long
descriptor PTE format.

So this patch introduces support for both long descriptor PTEs and HYP mode
registers.

Signed-off-by: Alexander Graf <agraf@suse.de>