Use extended crashkernel command line on x86_64

This patch removes the crashkernel parsing from
arch/x86_64/kernel/machine_kexec.c and calls the generic function, introduced
in the last patch, in setup_bootmem_allocator().

This is necessary because the amount of System RAM must be known in this
function now because of the new syntax.

Signed-off-by: Bernhard Walle <bwalle@suse.de>
Cc: Andi Kleen <ak@suse.de>
Cc: Vivek Goyal <vgoyal@in.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>