mtd: add missing MODULE_DESCRIPTION() macros

With ARCH=x86, make allmodconfig && make W=1 C=1 reports:
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/mtd/parsers/brcm_u-boot.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/mtd/parsers/tplink_safeloader.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/mtd/chips/cfi_util.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/mtd/chips/cfi_cmdset_0020.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/mtd/maps/map_funcs.o

Add the missing invocations of the MODULE_DESCRIPTION() macro.

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Acked-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20240610-md-drivers-mtd-v1-1-0f59183e4005@quicinc.com