riscv: dts: thead: Add TH1520 pin control nodes

riscv: dts: thead: Add TH1520 pin control nodes

Add nodes for pin controllers on the T-Head TH1520 RISC-V SoC.

Add the missing aonsys_clk for the always-on pin controller as there is
not yet an aon subsys clock controller driver.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Thomas Bonnefille <thomas.bonnefille@bootlin.com>
Signed-off-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
[dfustini: modify description as there is now an ap_subsys clk driver]
Signed-off-by: Drew Fustini <dfustini@tenstorrent.com>