spi: Tweak a few strange SPI NOR features for of-platdata

spi: Tweak a few strange SPI NOR features for of-platdata

The #define of one struct to another has been around for a while. It
confuses dtoc and makes it think that struct spi_flash does not exist.

Make a few changes to improve things while we wait for migration to be
completed:

- Move the 'struct spi_flash' to column 1 so dtoc scans it
- Remove the #define when compiling dt-platdata.c
- Update the strange mtd_get/set_of_node() functions
- Use struct spi_nor in the drivers, so dtoc sees the correct struct

Signed-off-by: Simon Glass <sjg@chromium.org>