mb/amd/chausie/chromeos.fmd: resize EC size in FMAP to 4kByte

Only the info about the location of the EC firmware will be stored right
at the beginning of the flash, so the size can be reduced to 4kByte
which is the erase block size of the flash. The CHAUSIE_MCHP_SIG_FILE
file itself is smaller than this.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: Icde5f7071183cd8423fc022caf49e2c9ee288527
Reviewed-on: https://review.coreboot.org/c/coreboot/+/62189
Reviewed-by: Fred Reitberger <reitbergerfred@gmail.com>
Reviewed-by: Jason Glenesk <jason.glenesk@gmail.com>
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/amd/chausie/chromeos.fmd

@@ -1,6 +1,6 @@
 FLASH@0xFF000000 16M {
 	SI_BIOS {
-		EC 128K
+		EC 4K
 		RW_MRC_CACHE(PRESERVE) 96K
 		RW_SECTION_A 3M {
 			VBLOCK_A 8K