target-xtensa: fix LOOPNEZ/LOOPGTZ translation

Translation of LOOP instructions used to call LEND SR write handler to
update LEND and invalidate relevant TBs. Now that LEND SR write handler
ends TB, LOOPNEZ and LOOPGTZ generate wrong code (same as for simple
LOOP). Fix it by calling wsr_lend helper directly.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
