Commit 8d5796d2ec6b5a4e7a52861144e63af438d6f8f7 allows for the vmalloc
area to be resized from the kernel cmdline. Make sure it cannot overlap
with RAM entirely.
Signed-off-by: Nicolas Pitre <nico@marvell.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>