nvmem: allow printing encrypted contents only in DEV images
nvmem: allow printing encrypted contents only in DEV images

The dump_nvmem CLI command used for debugging can also print out the
encrypted contents of the NVMEM objects in case it is passed any
command line parameter.

Let's limit this capability to DEV images only.

BRANCH=cr50, cr50-mp
BUG=none
TEST=verified that the contents still can be printed by images built
     with CR50_DEV.

Change-Id: I4e1204f2470b1481453ffd940102d8739b5d5a34
Signed-off-by: Vadim Bendebury <5515d6d2d0829cbe0dd0dcf2094aaded06d58514@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1779489
Reviewed-by: Mary Ruthven <81380f3403fed74252e92df3ed012a1819ec6296@chromium.org>

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