arm/mem_access: Introduce GENMASK_ULL bit operation

arm/mem_access: Introduce GENMASK_ULL bit operation

The current implementation of GENMASK is capable of creating bitmasks of
32-bit values on AArch32 and 64-bit values on AArch64. As we need to
create masks for 64-bit values on AArch32 as well, in this commit we
introduce the GENMASK_ULL bit operation. Please note that the
GENMASK_ULL implementation has been lifted from the linux kernel source
code.

Signed-off-by: Sergej Proskurin <proskurin@sec.in.tum.de>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>