From: Tom Rini <trini@kernel.crashing.org>

Various fixes for the PPC_GEN550 backend.

- Move PPC_GEN550 bool into a more appropriate spot.

- Add PPC_GEN550 support to the MCPN765 platform.

- Allow for SERIAL_TEXT_DEBUG on PPC_GEN550.

- Add missing headers to arch/ppc/syslib/gen550_dbg.c

- Clean-up the KGDB interface such that we allow for a kgdb_map_scc call,
  but do not require one.

- Add gen550 prototypes to <asm/kgdb.h>

- PPC_GEN550 backend code doesn't depend on 8250_SERIAL.