x86/kernel: Move page table macros to header

The PVH entry point will need an additional set of prebuild page tables.
Move the macros and defines to pgtable_64.h, so they can be re-used.

Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <20240823193630.2583107-5-jason.andryuk@amd.com>
Signed-off-by: Juergen Gross <jgross@suse.com>