kdump: use is_kdump_kernel() in sba_init()

o Make use of is_kdump_kernel() rather than checking elfcorehdr_addr directly.

o Remove CONFIG_CRASH_DUMP as is_kdump_kernel() is safe to call anywhere

o Remove CONFIG_PROC_FS as it is bogus, the check
  should occur regardless of if CONFIG_PROC_FS is set or not.

Signed-off-by: Simon Horman <horms@verge.net.au>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>