x86/mm/pat: Standardize on memtype_*() prefix for APIs

Half of our memtype APIs are memtype_ prefixed, the other half are _memtype suffixed:

	reserve_memtype()
	free_memtype()
	kernel_map_sync_memtype()
	io_reserve_memtype()
	io_free_memtype()

	memtype_check_insert()
	memtype_erase()
	memtype_lookup()
	memtype_copy_nth_element()

Use prefixes consistently, like most other modern kernel APIs:

	reserve_memtype()		=> memtype_reserve()
	free_memtype()			=> memtype_free()
	kernel_map_sync_memtype()	=> memtype_kernel_map_sync()
	io_reserve_memtype()		=> memtype_reserve_io()
	io_free_memtype()		=> memtype_free_io()

	memtype_check_insert()		=> memtype_check_insert()
	memtype_erase()			=> memtype_erase()
	memtype_lookup()		=> memtype_lookup()
	memtype_copy_nth_element()	=> memtype_copy_nth_element()

Signed-off-by: Ingo Molnar <mingo@kernel.org>