MIPS: AR7: Remove kgdb_enabled

An unused leftover from the old KGDB implementation.

Signed-off-by: Yoichi Yuasa <yuasa@linux-mips.org>
Patchwork: http://patchwork.linux-mips.org/patch/794/


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