mtd: spi-nor: intel-spi: Move platform data header to x86 subfolder

In order to group x86 related platform data move intel-spi.h to x86 folder.

While at it, remove duplicate inclusion in C file.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
[ta: s/x85/x86]
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20210304140820.56692-1-andriy.shevchenko@linux.intel.com