accel/ivpu: Add missing locks around mmu queues

Multiple threads were accessing mmu cmd queue simultaneously
causing sporadic failures in ivpu_mmu_cmdq_sync() function.
Protect critical code with mmu mutex.

Reviewed-by: Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>
Signed-off-by: Andrzej Kacprowski <Andrzej.Kacprowski@intel.com>
Signed-off-by: Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250204084622.2422544-2-jacek.lawrynowicz@linux.intel.com