arm64: rme: support RSI_HOST_CALL

Forward RSI_HOST_CALLS to KVM's HVC handler.

Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
---
Changes since v4:
 * Setting GPRS is now done by kvm_rec_enter() rather than
   rec_exit_host_call() (see previous patch - arm64: RME: Handle realm
   enter/exit). This fixes a bug where the registers set by user space
   were being ignored.