Move mt_init out of the way for the maple tree.  Use mips_mt prefix to
match the rest of the functions in the file.

Link: https://lkml.kernel.org/r/20220504002554.654642-2-Liam.Howlett@oracle.comSigned-off-by: NLiam R. Howlett <Liam.Howlett@oracle.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Howells <dhowells@redhat.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: SeongJae Park <sj@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>