MIPS: Delete unused file smp-gic.c

Commit 7eb8c99d ("MIPS: Delete smp-gic.c") removed the file from the
Makefile and the option to build it from KConfig, but left the file
itself floating in the tree.

Remove the unused source file.

Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com>
Cc: Qais Yousef <qsyousef@gmail.com>
Cc: paul.burton@imgtec.com
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/13883/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>