lmb: handle more than one DRAM BANK

lmb: handle more than one DRAM BANK

This fixes the automatic lmb initialization and reservation for boards
with more than one DRAM bank.

This fixes the CVE-2018-18439 and -18440 fixes that only allowed to load
files into the firs DRAM bank from fs and via tftp.

Found-by: Heinrich Schuchardt <[email protected]>
Signed-off-by: Simon Goldschmidt <[email protected]>
Tested-by: Heinrich Schuchardt <[email protected]>
Reviewed-by: Simon Glass <[email protected]>