build: add lpc source files
build: add lpc source files

Add lpc arch specific source file implementations to Makefile.  They
were accidentally left off.

Change-Id: I377d524e863620db273a92a3b6178d8e7a18a12d
Signed-off-by: Patrick Venture <36c53fa43f47f3fd67cb2fc38031827244d18a1f@google.com>

openbmc/phosphor-ipmi-flash