cr50: usb_updater: do not send setup request unless necessary
cr50: usb_updater: do not send setup request unless necessary

There are only two usb_updater actions which require establishing a
connection with the Cr50: transferring the firmware image during
update and reporting the version of the running image (because the
version is reported when the connection is established).

This patch refactors usb_updater code to establish the connection only
when necessary.

BRANCH=cr50
BUG=b:35587387,b:35587053
TEST=verified that 'usb_updater -c' succeeds both issued over USB and
      TPM

Change-Id: I6a0c82eb440c092263d4802f124f458f148a8ab5
Signed-off-by: Vadim Bendebury <5515d6d2d0829cbe0dd0dcf2094aaded06d58514@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/525095
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