meta-quanta: gbs: move to nuvoton-p2a-mbox PACKAGECONFIG

Use the PACKAGECONFIG option instead of setting the configure argument
directly.

Change-Id: I514138c63d58af1a0d83815241410a679a859d73
Signed-off-by: Benjamin Fair <benjaminfair@google.com>
diff --git a/meta-quanta/meta-gbs/recipes-phosphor/ipmi/phosphor-ipmi-flash_%.bbappend b/meta-quanta/meta-gbs/recipes-phosphor/ipmi/phosphor-ipmi-flash_%.bbappend
index 9f4c890..14f333b 100644
--- a/meta-quanta/meta-gbs/recipes-phosphor/ipmi/phosphor-ipmi-flash_%.bbappend
+++ b/meta-quanta/meta-gbs/recipes-phosphor/ipmi/phosphor-ipmi-flash_%.bbappend
@@ -1,5 +1,5 @@
 NUVOTON_FLASH_PCIMBOX = "0xF0848000"
 
-EXTRA_OECONF_append_gbs = " --enable-nuvoton-p2a-mbox"
+PACKAGECONFIG_append_gbs = " nuvoton-p2a-mbox"
 
 IPMI_FLASH_BMC_ADDRESS_gbs = "${NUVOTON_FLASH_PCIMBOX}"