Revert "lmb: Default to not-LMB_USE_MAX_REGIONS"

As explained by Philippe Schenker, I was misinterpreting what happened
in the case where we do not set LMB_USE_MAX_REGIONS and so had
re-introduced the problem I was attempting to more widely resolve.

This reverts commit 007ae5d1.

Reported-by: Philippe Schenker <philippe.schenker@toradex.com>
Signed-off-by: Tom Rini <trini@konsulko.com>