ALLWINNER generic config file and A31 kernel config

[manu_bidouilliste.com]

Summary

Add a ALLWINNER generic kernel config file, this build a kernel that works on A20 and A31.
Add a A31 kernel config file that include ALLWINNER and remove A20 support
Use ALLWINNER in A20 and remove A31 support
Move arm/allwinner/a20/if_dwc.c to if arm/allwinner/if_gmac.c
Add custom dts for BananaPi M2, this add the clock driver node and disable mmc2.

Test Plan

Apply patch and build kernel for A20 and A31 hardware.

[manu_bidouilliste.com]

After a discussion with jmcneill@ we decided to remove the A20 and A31 specific kernel config. It will be a pain to maintain as we adds more allwinner soc support.
Update release file to use the ALLWINNER kernel instead of the A20.

[manu_bidouilliste.com]

I'll update this rev once I've reworked D5573 to work with latest INTRNG bits so when we introduce the ALLWINNER kernel it will be for all Allwinner supported SoC.

[manu_bidouilliste.com]

There is still some stuff to do on A10 (INTRNG and DELAY) so update now.
This generic ALLWINNER kernel works on my A20-SOM-EVB, BananaPi M1 (A20) and Bananapi M2 (A31s)

[jmcneill]

sys/arm/allwinner/files.allwinner

20 ↗

(On Diff #15118)

How about aw_if_dwc.c?

[manu_bidouilliste.com]

Move if_gmac.c to aw_if_dwc.c
Add options SOC_ALLWINNER_A31S into ALLWINNER kernel

[manu_bidouilliste.com]

sys/arm/allwinner/files.allwinner

20 ↗

(On Diff #15118)

It's named like that for amlogic so I guess it make sense.