mm: Do not enable PG_arch_2 for all 64-bit architectures

Commit 4beba9486abd ("mm: Add PG_arch_2 page flag") introduced a new
page flag for all 64-bit architectures. However, even if an architecture
is 64-bit, it may still have limited spare bits in the 'flags' member of
'struct page'. This may happen if an architecture enables SPARSEMEM
without SPARSEMEM_VMEMMAP as is the case with the newly added loongarch.
This architecture port needs 19 more bits for the sparsemem section
information and, while it is currently fine with PG_arch_2, adding any
more PG_arch_* flags will trigger build-time warnings.

Add a new CONFIG_ARCH_USES_PG_ARCH_X option which can be selected by
architectures that need more PG_arch_* flags beyond PG_arch_1. Select it
on arm64.

Signed-off-by: Catalin Marinas <[email protected]>
[[email protected]: fix build with CONFIG_ARM64_MTE disabled]
Signed-off-by: Peter Collingbourne <[email protected]>
Reported-by: kernel test robot <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Steven Price <[email protected]>
Reviewed-by: Steven Price <[email protected]>
Signed-off-by: Marc Zyngier <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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