bits: split the definition of the asm and non-asm GENMASK*()

In an upcoming change, the non-asm GENMASK*() will all be unified to
depend on GENMASK_TYPE() which indirectly depend on sizeof(), something
not available in asm.

Instead of adding further complexity to GENMASK_TYPE() to make it work
for both asm and non asm, just split the definition of the two variants.

Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>