brcm63xx: use compatible instead of manually setting board name

brcm63xx: use compatible instead of manually setting board name

This patch removes the translation of device model name into a
board name in lib/brcm63xx.sh. The latter has been actually totally
useless as we have the compatible which can be used instead of
the board name (and actually is at other targets like ath79 or ramips).

The change requires updating the base-files with the new
identifiers based on compatible.

With all "board names" replaced by the compatible, we do not need
the old scripts to detect board name anymore and can also remove
the obsolete treatment of "legacy" devices without DTS, as there
are none of those left. So, this patch removes the target-specific
board detection and uses the standard procedure in
package/base-files/files/lib/preinit/02_sysinfo

This also fixes several cases where the board name was not set or
evaluated correctly:
- asmax,ar1004g in 02_network
- telsey,magic in 09_fix_crc/02_network
- brcm,bcm96338gw in 02_network
- brcm,bcm96338w in 02_network
- brcm,bcm96348gw in 02_network
- dynalink,rta1025w in 02_network
- huawei,echolife-hg520v in 02_network
- several cases in diag.sh

The following orphaned identifiers are removed from board.d files:
- dmv-s0

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>