linux-user: Fix executable page of /proc/self/maps

linux-user: Fix executable page of /proc/self/maps

The guest binary and libraries are not always map with the
executable bit in the host process. The guest may read a
/proc/self/maps with no executable address range. The
perm fields should be based on the guest permission inside
Qemu.

Signed-off-by: Nicolas Surbayrole <nsurbayrole@quarkslab.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Acked-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20210308091959.986540-1-nsurbayrole@quarkslab.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>