[PATCH] spi: handle spi-rx/tx-bus-width = 0 (no RX/TX line)

[r00tnomade]

Hey team,

I just put together a patch to fix that annoying "spi-rx-bus-width 0 not supported" warning we keep seeing on every boot for the Flipper One.

Turns out the Device Tree binding explicitly says a value of 0 means the line isn't wired up (like a write-only display with MISO left disconnected). However, spi_child_post_bind() was only looking for 1, 2, 4, or 8, so it threw a warning even though our DT is completely correct.

What I changed:

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Added the SPI_NO_RX and SPI_NO_TX flags to include/spi.h (matching Linux's naming convention).

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Handled the 0 case explicitly in drivers/spi/spi-uclass.c so it applies those flags instead of triggering the warning.

This should finally clear up the boot logs and close out issue #33. Let me know if it looks good to merge!

Best,

Sami