lmb: config: add lmb config symbols for SPL

lmb: config: add lmb config symbols for SPL

Add separate config symbols for enabling the LMB module for the SPL
phase. The LMB module implementation now relies on alloced list data
structure which requires heap area to be present. Add specific config
symbol for the SPL phase of U-Boot so that this can be enabled on
platforms which support a heap in SPL.

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