pinctrl: aspeed: Add AST2700 SoC0 pinctrl driver

The AST2700 is a dual-die BMC SoC: SoC0 (CPU die) and SoC1 (I/O die)
each have their own SCU with independent multi-function pin controls.

Add the pinctrl driver for the SoC0 die. The driver uses the generic
pinctrl framework and is compatible with the Linux kernel device tree
bindings, i.e. pin states are described with the same "function" and
"groups" properties and the same names as the Linux
aspeed,ast2700-soc0-pinctrl driver.

Unlike the older AST2500/AST2600 SCUs where each signal is enabled by
independent bits, the SoC0 mux selections mix single-bit enables
(eMMC, VGA DDC, VB strap), multi-bit selector fields (JTAG master port
select, USB2/USB3 port routing) and reset-control bits (PCIe RC
PERST). Model each (function, group) pair as one register
mask/value write so all of them fit a single flat table.

The gpio_request_enable hook releases the GPIO18A/GPIO18B pins to GPIO
mode by clearing every signal enable bit that claims the pin, matching
the Linux driver behaviour.

Signed-off-by: Billy Tsai <[email protected]>

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