target-xtensa: fix translation for opcodes crossing page boundary

If TB ends with an opcode that crosses page boundary and the following
page is not executable then EPC1 for the code fetch exception wrongly
points at the beginning of the TB. Always treat instruction that crosses
page boundary as a separate TB.

Cc: qemu-stable@nongnu.org
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>