test: lmb: tweak the tests for the persistent lmb memory map

The LMB memory maps are now persistent, with alloced lists being used
to keep track of the available and free memory. Make corresponding
changes in the test functions so that the list information can be
accessed by the tests for checking against expected values. Also
introduce functions to initialise and cleanup the lists. These
functions will be invoked from every test to start the memory map from
a clean slate.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Signed-off-by: Simon Glass <sjg@chromium.org>
[sjg: Use a stack to store pointer of lmb struct when running lmb tests]