libpayload;arch,cpu/x86: drop USE_MARCH_586 Kconfig option

Only the Intel Quark SoC selected this option and that SoC was dropped
in commit 531023285e ("soc/intel/quark: Drop support"), so drop this
Kconfig option too.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: Ic4f1c7530cd8ac7a1945b1493a2d53a7904daa06
Reviewed-on: https://review.coreboot.org/c/coreboot/+/75473
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

util/xcompile/xcompile

@@ -286,11 +286,7 @@ fi
 if [ "${TARCH}" = "x86_32" ]; then
 cat <<EOF
 
-ifneq (\$(CONFIG_USE_MARCH_586)\$(CONFIG_LP_USE_MARCH_586),)
-	CFLAGS_${TARCH} += -march=i586
-else
-	CFLAGS_${TARCH} += -march=i686
-endif
+CFLAGS_${TARCH} += -march=i686
 EOF
 fi