xtensa: fix str[n]cmp return value

str[n]cmp functions return negative value if the first string is less
than the second, positive value if the first string is greater than the
second and zero if they are equal. This is important when these
functions are used for sorting/binary search.

With incorrect strcmp return value bsearch was always failing in the
find_symbol_in_section making it impossible to load any module.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
xtensa: ISS: add host file-based simulated disk

Simdisk is a block device that maps to a file in the host file system.
It is usable for testing in the simulated environment, like xt-sim or
QEMU. Device binding to host file may be changed at runtime via proc
interface provided the device is not in use. Number of block devices
and initial binding to host files is controlled via kernel/module
parameters, with defaults specified in the kernel configuration.

Signed-off-by: Victor Prupis <vnp@tensilica.com>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>