charge_manager: Check extpower after charge port
charge_manager: Check extpower after charge port

Some platforms don't have an extpower interrupt and therefore use the
`board_check_extpower` function to determine if extpower is
actually present. Any time the EC changes its charge port selection, we
should re-evaluate the extpower as it likely has now changed.

This commit simply does the above.  Note that the default implementation
of `board_check_extpower` doesn't actually do anything, so this
should be a no-op for most boards.

BUG=b:187965740
BRANCH=dedede
TEST=Build and flash drawcia, verify that "AC on" prints are only
printed when we decide to charge from a port and not just when VBUS is
present

Signed-off-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@google.com>
Change-Id: Ib758b480a1e6f59f0f10caa1328b795726927f0b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2904546
Commit-Queue: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>
Tested-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@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