The idea is to panic() when there is no memory available for normal
operation. Exception: code which can consume arbitrary amount of RAM
(example: files allocated in ramfs) must report error instead of panic().

This patch also fixes code which didn't check for NULL from malloc() etc.

Usage: malloc(), memalign() return NULL when out of RAM.
xmalloc(), xmemalign() always return non-NULL or panic().

Signed-off-by: Krzysztof Hałasa <khc@pm.waw.pl>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>