MAINTAINERS: Add entry for SPI NAND framework and drivers

MAINTAINERS: Add entry for SPI NAND framework and drivers

In [1] Michael agreed on taking patches for SPI NAND through the RAW
NAND tree. Add a dedicated entry to the MAINTAINERS file which adds
Michael and Dario as maintainers and myself as reviewer.

[1] https://lists.denx.de/pipermail/u-boot/2023-February/508571.html

Signed-off-by: Frieder Schrempf <[email protected]>
Cc: Jagan Teki <[email protected]>
Cc: Dario Binacchi <[email protected]>
Cc: Michael Nazzareno Trimarchi <[email protected]>
Cc: Tom Rini <[email protected]>
Link: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Dario Binacchi <[email protected]>