target/mips: gdbstub: Revert commit 8e0b373f

Multiple reports from users were received regarding failures of
packet 'g' communication with gdb for some MIPS configurations.
It was found out (by bisecting) that the problematic commit is
8e0b373f. Revert that commit until a better solution is developed.

Suggested-by: Aleksandar Markovic <amarkovic@wavecomp.com>
Signed-off-by: Libo Zhou <zhlb29@foxmail.com>
Signed-off-by: Aleksandar Markovic <amarkovic@wavecomp.com>
Reviewed-by: Aleksandar Markovic <amarkovic@wavecomp.com>
Message-Id: <1568207966-25202-1-git-send-email-aleksandar.markovic@rt-rk.com>