[MIPS] kgdb: Remove existing implementation

This patch explicitly removes the kgdb implementation, for mips which
is intended to be followed by a patch that adds a kgdb implementation
for MIPS that makes use of the kgdb core in the kernel.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>