arm64: don't call break hooks for BRK exceptions from EL0

arm64: don't call break hooks for BRK exceptions from EL0

Our break hooks are used to handle brk exceptions from kgdb (and potentially
kprobes if that code ever resurfaces), so don't bother calling them if
the BRK exception comes from userspace.

This prevents userspace from trapping to a kdb shell on systems where
kgdb is enabled and active.

Cc: <stable@vger.kernel.org>
Reported-by: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
(cherry picked from commit c878e0cff5c5e56b216951cbe75f7a3dd500a736)
Signed-off-by: Mark Brown <broonie@kernel.org>
Conflicts:
	arch/arm64/kernel/debug-monitors.c