arm64: Make sure COMPAT_FREEBSD32 handles thumb entry point.

If the entry point for the binary executed is a thumb 2 entry point, make
sure we set the PSR_T bit, or the CPU will interpret it as arm32 code and
bad things will happen.

PR: 256899
MFC after: 1 week

(cherry picked from commit 712c060c94fd447c91b0e6218c12a431206b487a)
Signed-off-by: Olivier Houchard <cognet@FreeBSD.org>