ltq-adsl-mei: improve memory allocation

The ltq-adsl-mei driver allocates memory for the ADSL firmware in a
rather stupid way, leading to several 128k allocations, which fail when
many services are enabled. This patch tries to allocate 64 kiB chunks,
and only falls back to larger allocations if the returned pointers are
not correctly aligned. Fixes out-of-memory errors on Danube boards with
32 MiB RAM.

Signed-off-by: Matti Laakso <malaakso@elisanet.fi>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@40325 3c298f89-4303-0410-b956-a3cf2f4a3e73