Update of the Allwinner drivers to:

• Use the Linux compat string
• Use EARLY_DRIVER_MODULE to attach at the right time
• Add a generic A10 kernel config file
• A20 now use generic_timer
• Add two new dts files for Olimex boards
• Update our custom DTS file for A10 and A20 to use the same compatible property names as the vendor ones.

Submitted by: Emmanuel Vadot <manu@bidouilliste.com>
Differential Revision: https://reviews.freebsd.org/D4792