mm: introduce INVALID_{G,M}FN_RAW

mm: introduce INVALID_{G,M}FN_RAW

This allows properly tying together INVALID_{G,M}FN and
INVALID_{G,M}FN_INITIALIZER as well as using the actual values in
compile time constant expressions (or even preprocessor directives).

Since INVALID_PFN is unused, and with x86'es paging_mark_pfn_dirty()
being the only user of pfn_t it also doesn't seem likely that new uses
would appear, remove that one at this same occasion.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>