linux-user: xtensa: fix signal delivery in FDPIC

linux-user: xtensa: fix signal delivery in FDPIC

In FDPIC signal handlers are passed around as FD pointers. Actual code
address and GOT pointer must be fetched from memory by the QEMU code
that implements kernel signal delivery functionality. This change is
equivalent to the following kernel change:
9c2cc74fb31e ("xtensa: fix signal delivery to FDPIC process")

Cc: qemu-stable@nongnu.org
Fixes: d2796be69d7c ("linux-user: add support for xtensa FDPIC")
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>