The optee driver uses specific page table types to verify if a memory
region is normal. These types are not defined in nommu systems. Trying
to compile the driver in these systems results in a build error:

  linux/drivers/tee/optee/call.c: In function ‘is_normal_memory’:
  linux/drivers/tee/optee/call.c:533:26: error: ‘L_PTE_MT_MASK’ undeclared
     (first use in this function); did you mean ‘PREEMPT_MASK’?
     return (pgprot_val(p) & L_PTE_MT_MASK) == L_PTE_MT_WRITEALLOC;
                             ^~~~~~~~~~~~~
                             PREEMPT_MASK
  linux/drivers/tee/optee/call.c:533:26: note: each undeclared identifier is
     reported only once for each function it appears in
  linux/drivers/tee/optee/call.c:533:44: error: ‘L_PTE_MT_WRITEALLOC’ undeclared
     (first use in this function)
     return (pgprot_val(p) & L_PTE_MT_MASK) == L_PTE_MT_WRITEALLOC;
                                            ^~~~~~~~~~~~~~~~~~~

Make the optee driver depend on MMU to fix the compilation issue.
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
[jw: update commit title]
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>