lib/igt_map: Add 32-bit and 64-bit hash helper functions

Creating igt_map requires hashing and comparing function. Common case
is using 32-bit (like fd, etc.) or 64-bit keys (offsets) so adding
such helpers reduces code duplication.

Signed-off-by: Zbigniew Kempczyński <zbigniew.kempczynski@intel.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab@kernel.org>