Currently write_sysreg has to allocate a temporary register to write
zero to a system register, which is unfortunate given that the MSR
instruction accepts XZR as an operand.
Allow XZR to be used when appropriate by fiddling with the assembly
constraints.
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
7aff4a2dd3