apm821xx, ath79, ipq40xx, ipq806x, lantiq, ramips: base-files: Use generic diag.sh

apm821xx, ath79, ipq40xx, ipq806x, lantiq, ramips: base-files: Use generic diag.sh

I wanted to add status LEDs support to my imx6 based board and have found out,
that I could use diag.sh script found in ramips platform, which seems to be
also shared in a few other platforms:

 4801276bc2078c5bcf03003c831e3b0a target/linux/ramips/base-files/etc/diag.sh
 4801276bc2078c5bcf03003c831e3b0a target/linux/ipq40xx/base-files/etc/diag.sh
 4801276bc2078c5bcf03003c831e3b0a target/linux/ath79/base-files/etc/diag.sh

And @chunkeey suggested to me, that I can also add lantiq, ipq806x and
apm821xx to the list of platforms which could share this generic
diag.sh.

I've extended the base diag.sh in a way, that if it detects any of the
DTS LED aliases, then it would use the generic DTS set_led_state code.
The code in platform's diag.sh has moved to base-files package in this
commit:

 base-files: diag.sh: Make it more generic towards DTS so it could be reused

Signed-off-by: Petr Štetiar <ynezz@true.cz>
Tested-by: Christian Lamparter <chunkeey@gmail.com> (apm821xx and ipq40xx)
(backported from 9da6cd40ebb29c5d6d7af6af2c18b85448a28790)