arm64: gpr-num: support W registers

In subsequent patches we'll want to map W registers to their register
numbers. Update gpr-num.h so that we can do this.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20211019160219.5202-7-mark.rutland@arm.com


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