arm64: dts: rockchip: rock-3b: Model PI6C20100 as gated-fixed-clock

arm64: dts: rockchip: rock-3b: Model PI6C20100 as gated-fixed-clock

The Radxa ROCK 3B uses a PI6C20100 PCIe reference clock buffer to
provide a 100MHz reference clock to the PCIe 3.0 PHY and controllers.
This chip is currently modeled only as a fixed regulator
(vcc3v3_pi6c_03), with no clock output representation.

The PI6C20100 is a clock generator, not a power supply. Model it
properly as a gated-fixed-clock, following the pattern established
for the Rock 5 ITX and other boards with similar PCIe clock buffer
chips.

The gated-fixed-clock node references the regulator as its vdd-supply,
allowing the regulator to be enabled on demand. Remove the
regulator-always-on and regulator-boot-on properties from vcc3v3_pi6c_03
since the clock framework will manage the regulator lifecycle via
vdd-supply. The pcie3x2 node is updated to include the pipe and
reference clocks, matching the approach used in rk3588-rock-5-itx.dts.

Assisted-by: Claude:claude-3-opus
Signed-off-by: Midgy BALON <midgy971@gmail.com>
Link: https://patch.msgid.link/20260327091128.2458-1-midgy971@gmail.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>