Fix coding style issues reported by checkpatch.pl.
Signed-off-by: NMichal Simek <monstr@monstr.eu>

Just need to use little-endian opcode for brki r16, 0x18
Signed-off-by: NMichal Simek <monstr@monstr.eu>
CC: Jason Wessel <jason.wessel@windriver.com>

I forget to remove unused variable from kgdb_arch_handle_exception.
Fix return value in microblaze_kgdb_break function.

Error log:
arch/microblaze/kernel/kgdb.c: In function 'microblaze_kgdb_break':
arch/microblaze/kernel/kgdb.c:83: warning: 'return' with a value, in function returning void
arch/microblaze/kernel/kgdb.c: In function 'kgdb_arch_handle_exception':
arch/microblaze/kernel/kgdb.c:119: warning: unused variable 'cpu'
Signed-off-by: NMichal Simek <monstr@monstr.eu>

Kgdb uses brki r16, 0x18 instruction to call
low level _debug_exception function which save
current state to pt_regs and call microblaze_kgdb_break
function. _debug_exception should be called only from
the kernel space. User space calling is not supported
because user application debugging uses different handling.

pt_regs_to_gdb_regs loads additional special registers
which can't be changed

 * Enable KGDB in Kconfig
 * Remove ancient not-tested KGDB support
 * Remove ancient _debug_exception code from entry.S

Only MMU KGDB support is supported.
Signed-off-by: NMichal Simek <monstr@monstr.eu>
CC: Jason Wessel <jason.wessel@windriver.com>
CC: John Williams <john.williams@petalogix.com>
CC: Edgar E. Iglesias <edgar.iglesias@petalogix.com>
CC: linux-kernel@vger.kernel.org
Acked-by: NJason Wessel <jason.wessel@windriver.com>