mtd: cfi: allow building spi-intel standalone

When MTD or MTD_CFI_GEOMETRY is disabled, the spi-intel driver
fails to build, as it includes the shared CFI header:

include/linux/mtd/cfi.h:62:2: error: #warning No CONFIG_MTD_CFI_Ix selected. No NOR chip support can work. [-Werror=cpp]
   62 | #warning No CONFIG_MTD_CFI_Ix selected. No NOR chip support can work.

linux/mtd/spi-nor.h does not actually need to include cfi.h, so
remove the inclusion here to fix the warning. This uncovers a
missing #include in spi-nor/core.c so add that there to
prevent a different build issue.

Fixes: e23e5a05 ("mtd: spi-nor: intel-spi: Convert to SPI MEM")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Tokunori Ikegami <ikegami.t@gmail.com>
Acked-by: Pratyush Yadav <pratyush@kernel.org>
Reviewed-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20221220141352.1486360-1-arnd@kernel.org