staging: ralink-gdma: remove driver from tree

This driver was a added a time ago and there is no special effort or work
to clean it and any progress at all to mainline it. Also, the main user of
this dma controller seems to be 'i2s' in mt7621 SoCs. There is no in-tree
driver at all for the 'i2s' and its related device tree node has also been
deleted from main device tree file. Hence, remove this driver also for
completeness.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20211113192045.32153-2-sergio.paracuellos@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>