cr50: enable p256 curve for RMA unlock
cr50: enable p256 curve for RMA unlock

P256 key provisioning is complete, let's move RMA unlock to p256, this
frees up 5328 bytes in the flash.

BRANCH=cr50, cr50-mp
BUG=b:73296606
TEST=verified that dev key is properly accepted by the server, prod
      key will be tested when prod image is signed.

Change-Id: I7d86bb2b793c32181f47f5354ad9db603aa49881
Signed-off-by: Vadim Bendebury <5515d6d2d0829cbe0dd0dcf2094aaded06d58514@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1095535
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>

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