Use extended crashkernel command line on ppc64

This patch adapts the ppc64 code to use the generic parse_crashkernel()
function introduced in the generic patch of that series.

Signed-off-by: Bernhard Walle <bwalle@suse.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Vivek Goyal <vgoyal@in.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>