tigertail: fix USB timing
tigertail: fix USB timing

Add some disconnect time between mux selections.
This ensures that USB VBUS will fall and a USB
disconenct will happen.

BRANCH=None
BUG=b:35849284
TEST=ran on tigertail

Change-Id: I6cdbf8ce908f20213c7f8d1f4437ffe2b624be02
Reviewed-on: https://chromium-review.googlesource.com/459219
Commit-Ready: Nick Sanders <f4566bb3c90c0bf5fa0906b296b1da45051a62ee@chromium.org>
Tested-by: Nick Sanders <f4566bb3c90c0bf5fa0906b296b1da45051a62ee@chromium.org>
Reviewed-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>

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