The Xt is not part of the architectural name of the register
and it was likely added with the introduction of extended
register (Xt) TLBIs in Armv8 to differentiate them with
the old Armv7 ones.
The use of _Xt was not consistent anyway: newer TLBIs were
already omitting it.
Change-Id: Ic805340ffa7b5770e3b75a71bfb76e055e651f8b
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>