arm,smmu: match start level of page table walk with P2M

arm,smmu: match start level of page table walk with P2M

Don't hardcode the lookup start level of the page table walk to 1
and instead match the one used in P2M. This should fix scenarios
involving SMMU where the start level is different than 1.
In order for the SMMU driver to also compile on arm32 move the
P2M_ROOT_LEVEL in the p2m header file (while at it, for
consistency also P2M_ROOT_ORDER) and use the macro in the smmu
driver.

Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Acked-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>