KVM: x86/mmu: Use KMEM_CACHE instead of kmem_cache_create()

Use the new KMEM_CACHE() macro instead of direct kmem_cache_create
to simplify the creation of SLAB caches.

Note, KMEM_CACHE() uses the required alignment of the struct, '8' as the
alignment, whereas KVM's existing code passes '0'.  In the end, the two
values yield the same result as x86's minimum slab alignment is also '8'
(which is not at all coincidental).

Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
Link: https://lore.kernel.org/r/20240116100025.95702-1-chentao@kylinos.cn


[sean: call out alignment behavior]
Signed-off-by: Sean Christopherson <seanjc@google.com>