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>

src/arch/x86/Kconfig

@@ -92,12 +92,6 @@ config ARCH_X86_64_PGTBL_LOC
 	  The position where to place pagetables. Needs to be known at
 	  compile time. Must not overlap other files in CBFS.
 
-config USE_MARCH_586
-	def_bool n
-	help
-	  Allow a platform or processor to select to be compiled using
-	  the '-march=i586' option instead of the typical '-march=i686'
-
 # This is an SMP option. It relates to starting up APs.
 # It is usually set in mainboard/*/Kconfig.
 # TODO: Improve description.