x86, crashdump, /proc/vmcore: remove CONFIG_EXPERIMENTAL from kdump

I would suggest to remove the "experimental" status from Kdump.
Kdump is now in the kernel since a long time and used by Enterprise
distributions. I don't think that "experimental" is true any more.

Signed-off-by: Bernhard Walle <bwalle@suse.de>
Cc: vgoyal@redhat.com
Cc: kexec@lists.infradead.org
Cc: Bernhard Walle <bwalle@suse.de>
Cc: akpm@linux-foundation.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>