include/linux/crash_dump.h: add vmcore_cleanup() prototype

include/linux/crash_dump.h: add vmcore_cleanup() prototype

Eliminate the following warning in proc/vmcore.c:

  fs/proc/vmcore.c:1088:6: warning: no previous prototype for `vmcore_cleanup' [-Wmissing-prototypes]

[[email protected]: clean up powerpc, remove unneeded EXPORT_SYMBOL]
Signed-off-by: Rashika Kheria <[email protected]>
Reviewed-by: Josh Triplett <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>