mm: remove PMD alignment constraint in execmem_vmalloc()

When using vmalloc with VM_ALLOW_HUGE_VMAP flag, it will set the alignment
to PMD_SIZE internally, if it deems huge mappings to be eligible. 
Therefore, setting the alignment in execmem_vmalloc is redundant.  Apart
from this, it also reduces the probability of allocation in case vmalloc
fails to allocate hugepages - in the fallback case, vmalloc tries to use
the original alignment and allocate basepages, which unfortunately will
again be PMD_SIZE passed over from execmem_vmalloc, thus constraining the
search for a free space in vmalloc region.

Therefore, remove this constraint.

Link: https://lkml.kernel.org/r/20250918093453.75676-1-dev.jain@arm.com


Signed-off-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>