lmb: fix allocation at end of address range

The lmb code fails if base + size of RAM overflows to zero.

Fix this by calculating end as 'base + size - 1' instead of 'base + size'
where appropriate.

Added tests to assert this is fixed.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>