linux-user: Sanitize interp_info and, for mips only, init field fp_abi

linux-user: Sanitize interp_info and, for mips only, init field fp_abi

Sanitize interp_info structure in load_elf_binary() and, for MIPS only,
init its field fp_abi to MIPS_ABI_FP_UNKNOWN. This fixes appearances of
"Unexpected FPU mode" message in some MIPS use cases. Currently, this
bug is a complete stopper for some MIPS binaries.

In load_elf_binary(), struct image_info interp_info is used without
being properly initialized. One result is that when the ELF's program
header doesn't contain an entry for the ABI flags, then the value of
the struct image_info's fp_abi field is set to whatever happened to
be in stack memory at the time.

Backporting to 4.0 and, if possible, to 3.1 is recommended.

Fixes: https://bugs.launchpad.net/qemu/+bug/1825002
Signed-off-by: Daniel Santos <daniel.santos@pobox.com>
Signed-off-by: Aleksandar Markovic <amarkovic@wavecomp.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <1558282527-22183-6-git-send-email-aleksandar.markovic@rt-rk.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>