lib: remove FLASHMAP_OFFSET config variable

The FLASHMAP_OFFSET config variable is used in lib/fmap.c, however
the fmdtool creates a fmap_config.h with a FMAP_OFFSET #define.
Those 2 values are not consistent. Therefore, remove the Kconfig
variable and defer to the #define generated by fmdtool.

Change-Id: Ib4ecbc429e142b3e250106eea59fea1caa222917
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/14765
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Leroy P Leahy <leroy.p.leahy@intel.com>

src/mainboard/google/nyan/Kconfig

@@ -82,10 +82,6 @@ config EC_GOOGLE_CHROMEEC_SPI_BUS
 	hex
 	default 1
 
-config FLASHMAP_OFFSET
-	hex
-	default 0x00100000
-
 config DRIVER_TPM_I2C_BUS
 	hex
 	default 0x2