nocturne: Don't enter DP Alt Mode when AP is off.
nocturne: Don't enter DP Alt Mode when AP is off.

According to the DisplayPort Alt Mode on USB Type-C specification, if
the DisplayPort Source device does not need to maintain HPD connectivity
information prior to entering a low power state, the device shall exit
the DP Alternate Mode.  Previously, we were always entering DP Alt Mode
regardless of the SoC state.  When we are shutting the device down to S5
or G3, there's no need to monitor the HPD connectivity information.

This commit simply does not enter DP Alt Mode when the SoC is off.

BUG=chromium:927636
BRANCH=firmware-nocturne-10984.B
TEST=Flash nocturne, shut DUT down to S5/G3, plug in a USB-C monitor
that can also act as a Source, verify with PD analyzer that DUT does not
Enter DP Alt mode, boot system up, verify that external display works.

Change-Id: I2ad3619cabeae5d90e8af1bfa9cab67452d9fc16
Signed-off-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1450815
Reviewed-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>
Tested-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>
Commit-Queue: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>

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