cr50: Check if inactive RW region needs to be invalidated
cr50: Check if inactive RW region needs to be invalidated

There is no need to invalidate the inactive RW image if it's already
been done. Check the magic area of the header and if already 0s, then
set *response_size and return VENDOR_RC_SUCCESS.

BUG=chrome-os-partner:62588
BRANCH=none
TEST=manual
Update H1 FW on Eve. Using 'ver' command verify that it has valid A/B
RW images. Log into chromeos and see console messages indicating that
inactive image is being invalidated and via 'ver' command. Reboot via
H1 console and see that this time the message
vc_invalidate_inactive_rw: Inactive region already corrupted
is displayed.

Change-Id: I0894d456fdc63f64fc7272ad55d75ba94dbe94c4
Signed-off-by: Scott <7d40b3eb9e17bf55d972074a5e77a7ea4159f9dd@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/438787
Commit-Ready: Scott Collyer <7d40b3eb9e17bf55d972074a5e77a7ea4159f9dd@chromium.org>
Tested-by: Scott Collyer <7d40b3eb9e17bf55d972074a5e77a7ea4159f9dd@chromium.org>
Reviewed-by: Vadim Bendebury <5515d6d2d0829cbe0dd0dcf2094aaded06d58514@google.com>

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