x86/mm: Always "broadcast" PMD setting operations

x86/mm: Always "broadcast" PMD setting operations

Kernel PMDs can either be shared across processes or private to a
process.  On 64-bit, they are always shared.  32-bit non-PAE hardware
does not have PMDs, but the kernel logically squishes them into the
PGD and treats them as private. Here are the four cases:

	64-bit:                Shared
	32-bit: non-PAE:       Private
	32-bit:     PAE+  PTI: Private
	32-bit:     PAE+noPTI: Shared

Note that 32-bit is all "Private" except for PAE+noPTI being an
oddball.  The 32-bit+PAE+noPTI case will be made like the rest of
32-bit shortly.

But until that can be done, temporarily treat the 32-bit+PAE+noPTI
case as Private. This will do unnecessary walks across pgd_list and
unnecessary PTE setting but should be otherwise harmless.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/20250414173235.F63F50D1%40davehans-spike.ostc.intel.com