vboot: rename VbExGetSwitches to vb2ex_physical_presence_pressed

The only purpose of this function is to get the physical presence
switch.  Rename it appropriately, and migrate function header
into 2api.h.

BUG=b:124141368, chromium:1035761
TEST=Build locally
BRANCH=none

Change-Id: Ice3e3a362ca2d2e3aa18c60a129f67d5139daf04
Cq-Depend: chromium:2069629
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2069628
Tested-by: Joel Kitching <kitching@chromium.org>
Reviewed-by: Yu-Ping Wu <yupingso@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Commit-Queue: Joel Kitching <kitching@chromium.org>
8 files changed