tcpci: Handle alerts in tcpci_tcpm_init()
tcpci: Handle alerts in tcpci_tcpm_init()

tcpci_tcpm_init() was clearing all alerts without handling them.
The nct38xx is combined TCPC and IO expander. IO expander interrupts
(IOEX_INT) rely on TCPC_REG_ALERT_VENDOR_DEF. This alert was being lost
because tcpci_tcpm_init() was clearing it when we came out of low power
mode in response to the alert interrupt from the TCPC.

BUG=b:146468190
BRANCH=none
TEST=IOEX_INT works with TCPC exiting low power mode
TEST=Init, source, sink, low power all still work with ANX3429, ANX7447,
     PS8751, NCT3807 TCPCs

Change-Id: I8ea4907ff621c4f39284a400fc40f2a20bf3ce91
Signed-off-by: Edward Hill <db1406b34e091703092b6b136bdfeb2c8125fc0e@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2031650
Reviewed-by: Denis Brockus <6b21e8190fb5e373363fb95271367073a16474ef@chromium.org>
Reviewed-by: Diana Z <cb2016afc7183e5356c690dc63b4ba817470501a@chromium.org>

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