xtensa: add __umulsidi3 helper

xtensa gcc-13 has changed multiplication handling and may now use
__umulsidi3 helper where it used to use __muldi3. As a result building
the kernel with the new gcc may fail with the following error:

    linux/init/main.c:1287: undefined reference to `__umulsidi3'

Fix the build by providing __umulsidi3 implementation for xtensa.

Cc: stable@vger.kernel.org # 5.18+
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>