Remove dra7xx-evm machine support

Remove dra7xx-evm machine support

Remove dra7xx-evm machine template and related BSP configuration
tweaks.  The configuration is stale and untested, and no one has
expressed interest in it for long enough that it seems better to
just remove it to avoid confusion about support status.

Bug-AGL: SPEC-3934

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: I1659eef113cf1e6fcfdddf65f712275b8fc49b6f
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/26378
Tested-by: Jenkins Job builder account
ci-image-build: Jenkins Job builder account
ci-image-boot-test: Jenkins Job builder account
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>