twinkie: fix sink firmware
twinkie: fix sink firmware

add a dummy pd_custom_vdm() function to be able to build again a Twinkie
firmware in "PD sink" mode.

Signed-off-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

BRANCH=none
BUG=none
TEST=./board/twinkie/build_rw_variant

Change-Id: Ib0f82ecd1197300cf7b36f0f43c6b1cd03203557
Reviewed-on: https://chromium-review.googlesource.com/239234
Reviewed-by: Alec Berg <1a4429eeda29095a12e19a73405f80f5b7f37a63@chromium.org>
Tested-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>
Commit-Queue: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

fourier49/BIZ_EC,coreboot/chrome-ec,fourier49/BZ_DEV_EC,md5555/ec,coreboot/chrome-ec,md5555/ec,md5555/ec,coreboot/chrome-ec,mtk09422/chromiumos-platform-ec,fourier49/BIZ_EC,mtk09422/chromiumos-platform-ec,fourier49/BZ_DEV_EC,akappy7/ChromeOS_EC_LED_Diagnostics,akappy7/ChromeOS_EC_LED_Diagnostics,eatbyte/chromium-ec,fourier49/BIZ_EC,mtk09422/chromiumos-platform-ec,akappy7/ChromeOS_EC_LED_Diagnostics,eatbyte/chromium-ec,coreboot/chrome-ec,coreboot/chrome-ec,md5555/ec,coreboot/chrome-ec,fourier49/BZ_DEV_EC,fourier49/BIZ_EC,eatbyte/chromium-ec,eatbyte/chromium-ec,akappy7/ChromeOS_EC_LED_Diagnostics,akappy7/ChromeOS_EC_LED_Diagnostics,fourier49/BZ_DEV_EC,mtk09422/chromiumos-platform-ec