configs: lito: Add platform_lpi_enable flag

On lito, it is assumed that all sessions will have the same setting
for LPI enablement. So this flag will move from each individual
sound_model_config to the common_config.

Change-Id: Iee1366513154ffa78894be2c8d40b06f712c71ff
Signed-off-by: Vatsal Bucha <vbucha@codeaurora.org>