pd: RCH_Processing_Extended_Message cleanup
pd: RCH_Processing_Extended_Message cleanup

Change first chunk processing to be handled embedded in
RCH_Wait_For_Message_From_Protocol_Layer run to get the
actual first chunk and don't rely on the chunk headers
to indicate the first chunk

BUG=none
BRANCH=none
TEST=make buildall -j

Change-Id: Iadb606dfaca7b3f4d3ff6528dcfbd3e6aad196a4
Signed-off-by: Denis Brockus <6b21e8190fb5e373363fb95271367073a16474ef@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1773118

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec