Although M profile doesn't have the same concept of exception level
as A profile, it does have a notion of privileged versus not, which
we currently track in the privmode TB flag. Support returning this
information if arm_current_el() is called on an M profile core, so
that we can identify the correct MMU index to use (and put the MMU
index in the TB flags) without having to special-case M profile.
Backports commit 6d54ed3c93f1e05a483201b087142998381c9be8 from qemu