pd: do not respond to unknown SVDMs
pd: do not respond to unknown SVDMs

bug fix: if we see an unknown SVDM, do not respond to it.

BUG=none
BRANCH=samus
TEST=test with third party that sends unknown SVDM

Change-Id: I3ef6c38be029d57bf3784ba832b7ae137f379049
Signed-off-by: Alec Berg <1a4429eeda29095a12e19a73405f80f5b7f37a63@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/224179
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

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