soc: apple: Add hardware tunable support

soc: apple: Add hardware tunable support

Various hardware, like the Type-C PHY or the Thunderbolt/USB4 NHI,
present on Apple SoCs need machine-specific tunables passed from our
bootloader m1n1 to the device tree. Add generic helpers so that we
don't have to duplicate this across multiple drivers.

Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Neal Gompa <neal@gompa.dev>
Reviewed-by: Janne Grunau <j@jannau.net>
Signed-off-by: Sven Peter <sven@kernel.org>
Link: https://patch.msgid.link/20251214-b4-atcphy-v3-1-ba82b20e9459@kernel.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>