drm/xe/mmio: Use non-atomic writeq/readq variant for 32b

writeq() and readq() and other functions working on 64 bit variables
are not provided by 32b arch. For that it's needed to choose between
linux/io-64-nonatomic-hi-lo.h and linux/io-64-nonatomic-lo-hi.h,
spliting the read/write in 2 accesses. For xe driver, it doesn't matter
much, so just choose one and include in xe_mmio.h.

This also removes some ifdef CONFIG_64BIT we had around because of the
missing 64bit functions.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>