KVM: selftests: Move PTE bitmasks to kvm_mmu

KVM: selftests: Move PTE bitmasks to kvm_mmu

Move the PTE bitmasks into kvm_mmu to parameterize them for virt mapping
functions. Introduce helpers to read/write different PTE bits given a
kvm_mmu.

Drop the 'global' bit definition as it's currently unused, but leave the
'user' bit as it will be used in coming changes. Opportunisitcally
rename 'large' to 'huge' as it's more consistent with the kernel naming.

Leave PHYSICAL_PAGE_MASK alone, it's fixed in all page table formats and
a lot of other macros depend on it. It's tempting to move all the other
macros to be per-struct instead, but it would be too much noise for
little benefit.

Keep c_bit and s_bit in vm->arch as they used before the MMU is
initialized, through  __vmcreate() -> vm_userspace_mem_region_add() ->
vm_mem_add() -> vm_arch_has_protected_memory().

No functional change intended.

Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
[sean: rename accessors to is_<adjective>_pte()]
Link: https://patch.msgid.link/20251230230150.4150236-10-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>