lmb: add logic to print lmb flag strings

Instead of printing the LMB flags as numerical values, print them as
strings. This makes it easier to understand what flags are associated
with the lmb region. Also make corresponding changes to the bdinfo
command's test code.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>