tests/tcg/xtensa: restore vecbase SR after test

Writing garbage into the vecbase SR results in hang in the subsequent
tests that expect to raise an exception. Restore vecbase SR to its
reset value after the test.

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

tests/tcg/xtensa/test_sr.S

@@ -221,6 +221,8 @@ test_sr_mask /*scompare1*/12, 0, 0
 
 #if XCHAL_HAVE_VECBASE
 test_sr vecbase, 1
+movi	a2, XCHAL_VECBASE_RESET_VADDR
+wsr	a2, vecbase
 #else
 test_sr_mask /*vecbase*/231, 0, 0
 #endif