mb/amd/chausie: change AMD_FWM_POSITION_INDEX for non-chromeos case

Commit 2c102232e8 ("mb/amd/chausie,google/skyrim: increase
RW_MRC_CACHE size to 120 kByte") increased the MRC cache size, but with
the change the default AMD_FWM_POSITION_INDEX which is 5 for the 16MByte
flash size, the amdfw part won't be placed on the expected position,
since the cbfs header is in that exact location and cbfstool places the
amdfw part right after that. Change the AMD_FWM_POSITION_INDEX to 4 for
the non-chromeos builds to work around this.

TEST=Non-chromeos chausie build now boots and doesn't fail any more
before releasing the x86 cores from reset

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: I89fe1d0672139e04070f05c6c8fa8955edcfc7ee
Reviewed-on: https://review.coreboot.org/c/coreboot/+/70133
Reviewed-by: Fred Reitberger <reitbergerfred@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/amd/chausie/Kconfig

@@ -29,6 +29,7 @@ config MAINBOARD_PART_NUMBER
 config AMD_FWM_POSITION_INDEX
 	int
 	default 3 if CHROMEOS
+	default 4
 	help
 	  TODO: might need to be adapted for better placement of files in cbfs