mb/amd/mandolin: simplify flashmap file

Now that we're using fmaptool to parse the .fmd file, we can use some
short forms and omit unnecessary information.

BUG=b:157068645
TEST=Timeless build for amd/mandolin resulted in identical binary.
BRANCH=zork

Change-Id: I196c7857f165e75b543c1bda650e044b5ad0664e
Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/45596
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/mainboard/amd/mandolin/variants/mandolin/board.fmd

@@ -1,7 +1,7 @@
-FLASH@0xFF800000 0x800000 {
+FLASH@0xFF800000 8M {
-	BIOS@0x0 {
+	BIOS {
-		EC@0x0 0x20000
+		EC 0x20000
-		RW_MRC_CACHE@0x20000 0x10000
+		RW_MRC_CACHE 64K
 		FMAP 0x1000
 		COREBOOT(CBFS)
 	}