aw_gpio: support Allwinner D1 GPIO

The GPIO controls the multiplexing of the D1 pins to its peripherals,
so this adds the definitions needed by the aw_gpio driver to support
the D1.

Also, this modifies the aw_gpio driver to support the differences of
the D1 controller:

• pins can have up to 15 functions
• each port is mapped with an alignment of 0x30
• CFG registers have 4 bits per pin
• DRV registers have 4 bits per pin
• the offset of PULL registers is 0x24

Signed-off-by: Julien Cassette <julien.cassette@gmail.com>
Reviewed by: mhorne
Differential Revision: https://reviews.freebsd.org/D35593