pinctrl: aspeed: Add multiple pin group support for functions

The AST2400 and AST2500 SoCs only exposed one pin group per function.
Lone pin groups drove some implementation simplifications in the ASPEED
pinmux infrastructure that is now invalid for the AST2600, which
supports multiple groups per function for some functions on the chip
(SMBus Alert pins and UARTs among others).

This patch reworks the macro jungle to enable support for multiple pin
groups. In the process we inflict some collateral damage on the existing
AST2400 and AST2500 drivers, but the rework is mostly a relatively
straight-forward, automated transform of adding the pin name as an
argument to some macro calls and implementing wrappers to paper over
groups in the cases where there aren't multiple.

As previously documented, the macro infrastructure exposes mux
configuration as symbols in the source file which are used to detect
accidental duplication. Previously these symbols were named in terms of
the signal for a given expression. As the AST2600 supports multiple pin
groups for a function, the signal name on its own is no-longer unique,
and we must switch to the (signal, group) tuple. However, this means
that we can no-longer derive the signal expression symbol name from the
signal name alone, which among other cases, impacts the operation of the
PIN_DECL_x() macros.

To fix that and avoid requiring we awkwardly provide the associated
group name for every signal for every PIN_DECL_x() invocation, instead
opportunistically alias the name of the signal expression symbol from
the unique (signal, group) tuple to the also unique (pin, signal) tuple,
then reference the alias symbol in the tables generated by PIN_DECL_x().
This way we do not require extra group parameters for PIN_DECL_x() as
the pin name was already provided as an argument, and instead simply
require that the pin name be provided to the expression declaration
macros in order to generate the alias symbol.

The patch implements the alias strategy and fixes up all the expression
definition macro calls in the AST2400 and AST2500 drivers to account for
pin groups. Given the implementation strategy has the property that
compilation either fails or loudly warns for bad pin descriptions, this
patch is theoretically tested by successfully compiling both affected
drivers. For a more practical test I've inspected the diff of the
content of the pinctrl debugfs entries before and after the patch under
qemu; all pins, functions and groups match.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Link: https://lore.kernel.org/r/20190729055604.13239-5-andrew@aj.id.au
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>