memtest: By default only test biggest region ...

Often enough the biggest free region spans most free RAM, so
it doesn't add much value to test the remaining free regions. This
patch changes the default behaviour to only test the biggest free
region and adds the -t option to test all regions.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

memtest: split tests in separate functions ...

The memtest does a bus integrity check and a moving inversions test.
Split the tests into two separate functions so that the can be called
separately.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

memtest: move request/release regions to common/ ...

Normally code providing a feature should be implemented in common/ which
is then called from the command code. Follow this rule and move some more
of the memtest code to common/.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

common: add memtest.c with mem_test routine ...

Add mem_test routine. Useful to detect timing problems if someone
porting a new device to barebox. This test includes a data bus test,
address bus test and integrity check of memory.

This mem_test routine has as parameter start and end address of testing
space. The last parameter can skip the integrity check.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>