mm/hmm: make CONFIG_HMM_MIRROR select CONFIG_MMU_NOTIFIER

hmm doesn't currently build well with MMU_NOTIFIER=n:

With microblaze
https://download.01.org/0day-ci/archive/20260702/202607021433.DYT5fDqE-lkp@intel.com/config
(CONFIG_MMU_NOTIFIER=n):

mm/hmm.c: In function 'hmm_range_fault_unlocked_timeout':
mm/hmm.c:804:25: error: implicit declaration of function 'mmu_interval_read_begin'; did you mean 'mmu_interval_check_retry'? [-Wimplicit-function-declaration]
  804 |                         mmu_interval_read_begin(range->notifier);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~
      |                         mmu_interval_check_retry

Quoting Stanislav:

:  Documentation/mm/hmm.rst explicitly states:
: 
:  "Address space mirroring's main objective is to allow duplication of a
:  range of CPU page table into a device page table; HMM helps keep both
:  synchronized.  A device driver that wants to mirror a process address
:  space must start with the registration of a mmu_interval_notifier"
: 
:  I think making CONFIG_HMM_MIRROR dependent on the CONFIG_MMU_NOTIFIER
:  is the right thing to do.

So select MMU_NOTIFIER if hmm.c is to be compiled.

Cc: David Hildenbrand <david@kernel.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Stanislav Kinsburskii <skinsburskii@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/Kconfig

@@ -1252,6 +1252,7 @@ config ZONE_DEVICE
 config HMM_MIRROR
 	bool
 	depends on MMU
+	select MMU_NOTIFIER
 
 config GET_FREE_REGION
 	bool