rockchip: explicitly specify pine64_rockpro64 supported devices

rockchip: explicitly specify pine64_rockpro64 supported devices

The board name that goes into /etc/board.json and is used by sysupgrade
for image verifications gets determined by the below command:

  `strings /proc/device-tree/compatible | head -1`

as per package/base-files/files/lib/preinit/02_sysinfo

On more recent firmware version for the Pine64 RockPro64 v2.1 devices the
first entry is 'pine64,rockpro64-v2.1' however the metadata in the
sysupgrade image only specifies 'pine64,rockpro64' as supported and image
verification will fail.

This change makes it so the image metadata will contain both
'pine64,rockpro64' and 'pine64,rockpro64-v2.1' allowing image verification
to pass on both older and more recent firmware versions.

Signed-off-by: Sam Hegarty <hegarty.sam@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/18542
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>