pinctrl: Port pin controller driver for T-Head TH1520 SoC

pinctrl: Port pin controller driver for T-Head TH1520 SoC

The SoC pads of TH1520 are separated into three groups (AP 1, AP 2 and
AON) controlled by independent pin controllers. This patch ports their
driver from Linux kernel with most code for setting pinconf and pinmux
kept as is.

The dt-binding of TH1520 pin controller uses a schema where pins to
configure are specfied as strings and looked up at runtime, which the
generic pinctrl helpers of U-Boot cannot parse, thus a customized
set_state() callback is implemented to parse pinconfig nodes and setup
the configuration.

Signed-off-by: Yao Zi <ziyao@disroot.org>
Acked-by: Leo Yu-Chi Liang <ycliang@andestech.com>