staging: mt7621-dts: use valid vendor 'mediatek' instead of invalid 'mtk'

staging: mt7621-dts: use valid vendor 'mediatek' instead of invalid 'mtk'

Vendor listed for mediatek in kernel vendor file 'vendor-prefixes.yaml'
contains 'mediatek' as a valid vendor string. Some nodes in the device
tree are using an invalid vendor string vfor 'mtk' instead. Fix all of
them in dts file. Update also ralink mt7621 related code to properly
match new strings. Even there are used in the device tree there are
some strings that are not referred anywhere but have been also updated
with new vendor name. These are 'mtk,mt7621-wdt', 'mtk,mt7621-nand',
'mtk,mt7621-mc', and 'mtk,mt7621-cpc'.

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20210410055059.13518-4-sergio.paracuellos@gmail.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>