payloads/edk2: Add note that upstream edk2 does not work

Upstream edk2 doesn't work, but we still have the option for it
for testing.

Signed-off-by: Sean Rhodes <sean@starlabs.systems>
Change-Id: I6ec9f4746640baa030762650ab7b83d85ab8c1e1
Reviewed-on: https://review.coreboot.org/c/coreboot/+/67780
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Lean Sheng Tan <sheng.tan@9elements.com>
diff --git a/payloads/external/edk2/Kconfig b/payloads/external/edk2/Kconfig
index f753ad9..e0c19bb 100644
--- a/payloads/external/edk2/Kconfig
+++ b/payloads/external/edk2/Kconfig
@@ -33,6 +33,8 @@
 	  Select this option if you want to use the official edk2 repository to build
 	  edk2.
 
+	  Please note, this option will not work on any SOC without modification.
+
 config EDK2_REPO_CUSTOM
 	bool "Specify your own repository"
 	help