Split MAYBE_STATIC to _BSS and _NONZERO variants

These are required to cover the absensce of .data and
.bss sections in some programs, most notably ARCH_X86
in execute-in-place with cache-as-ram.

Change-Id: I80485ebac94b88c5864a949b17ad1dccdfda6a40
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35003
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/device/device_const.c

@@ -204,7 +204,7 @@ DEVTREE_CONST struct device *pcidev_path_on_bus(unsigned int bus, pci_devfn_t de
 DEVTREE_CONST struct bus *pci_root_bus(void)
 {
 	DEVTREE_CONST struct device *pci_domain;
-	MAYBE_STATIC DEVTREE_CONST struct bus *pci_root = NULL;
+	MAYBE_STATIC_BSS DEVTREE_CONST struct bus *pci_root = NULL;
 
 	if (pci_root)
 		return pci_root;