pinctrl: rockchip: add support for RK3308B SoC

The RK3308B is a revision of the RK3308 including different iomux
register layout.
Several pins (GPIO2_A2, GPIO2_A3, GPIO2_C0, GPIO3_B2, GPIO3_B3)
have 3-bit mux fields in new GRF registers (SOC_CON13 at 0x608 and
SOC_CON15 at 0x610) that override the standard 2-bit fields.
I believe the bootloader sets the sel_src_ctrl bits to activate these
new registers, which causes the kernel's writes to the old 2-bit iomux
registers to be silently ignored.

Without this patch, SPI1, I2C3, and other peripherals that depend on
these pins are completely non-functional on my RK3308B boards.

Detect the SoC variant at runtime by reading the chip_id register at GRF
offset 0x800 (0xcea = RK3308, 0x3308/0x3308c = RK3308B), as requested
by reviewers of the earlier series.
When RK3308B is detected, swap in the correct mux_recalced and mux_route
tables and write the sel_src_ctrl bits to ensure the 3-bit mux registers
are active.

This is a rework of Dmitry Yashin's series [1] which used a separate
device tree compatible string ("rockchip,rk3308b-pinctrl") to
distinguish the variants.
Reviewers Luca Ceresoli and Heiko Stuebner agreed that runtime detection
was preferable since boards are manufactured with both RK3308 and RK3308B
using the same device tree.

Jonas Karlman implemented runtime detection based on the GRF_CHIP_ID
register [2]. Reviewers asked for more changes (constifying some
arrays), but the series was never resubmitted and was dropped.

I run this patch on my Rock Pi S boards, the newer ones I've got in
2024 use the RK3308B. And thanks to runtime detection we should still
be compatible with older devices (but I couldn't test on RK3308 as I
don't have any).

[1] https://lore.kernel.org/all/20240515121634.23945-1-dmt.yashin@gmail.com/
[2] https://lore.kernel.org/all/20240604141020.21725-1-dmt.yashin@gmail.com/

Signed-off-by: Hugo VALTIER <hugo@ahdrone.com>
Tested-by: Dmitry Yashin <dmt.yashin@gmail.com>
Signed-off-by: Linus Walleij <linusw@kernel.org>

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