arm64: entry: consolidate EL1 exception returns

Following the example of ret_to_user, let's consolidate all the EL1
return paths with a ret_to_kernel helper, rather than each entry point
having its own copy of the return code.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20210607094624.34689-11-mark.rutland@arm.com


Signed-off-by: Will Deacon <will@kernel.org>