linux-postmarketos-omap: support nokia n900

Notes:

• replaces !3915 (closed)
• 0007-ARM-dts-N900-use-iio-driver-for-accelerometer.patch is upstream as of linux 6.3-rc1, so will be dropped from the package in near future
• once merged, I will submit another MR switching the n900 device package over to linux-postmarketos-omap and dropping the linux-nokia-n900 package

@MightyM17 & @antoni.aloytorrens please test again :-)