lmb: check if a region can be reserved by lmb_reserve()

lmb: check if a region can be reserved by lmb_reserve()

The logic used in lmb_alloc() takes into consideration the existing
reserved regions, and ensures that the allocated region does not
overlap with any existing allocated regions. The lmb_reserve()
function is not doing any such checks -- the requested region might
overlap with an existing region. This also shows up with
lmb_alloc_addr() as this function ends up calling lmb_reserve().

Add a function which checks if the region requested is overlapping
with an existing reserved region, and allow for the reservation to
happen only if both the regions have LMB_NONE flag, which allows
re-requesting of the region. In any other scenario of an overlap, have
lmb_reserve() return -EEXIST, implying that the requested region is
already reserved.

Add corresponding test cases which check for overlapping reservation
requests made through lmb_reserve() and lmb_alloc_addr(). And while
here, fix some of the comments in the test function being touched.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>