ARM: 5989/1: ARM: KGDB: add support for SMP platforms

ARM: 5989/1: ARM: KGDB: add support for SMP platforms

To support SMP platforms, KGDB requires the architecture backend to
implement the kgdb_roundup_cpus function.

This patch, taken against 2.6.33, implements the function for ARM based
on the MIPS port.

Cc: Jason Wessel <jason.wessel@windriver.com>
Cc: Jean-Michel Hautbois <jhautbois@gmail.com>
Cc: KGDB Mailing List <kgdb-bugreport@lists.sourceforge.net>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>