spl: fix build failure with !CONFIG_SPL_PCI_SUPPORT

Building U-Boot with CONFIG_PCI and CONFIG_DM_PCI enabled, but
CONFIG_SPL_PCI_SUPPORT disabled, results in following linker
error:

lib/built-in.o: In function `fdtdec_get_pci_bar32':
lib/fdtdec.c:305: undefined reference to `dm_pci_read_bar32'
fdtdec.c:305:(.text.fdtdec_get_pci_bar32+0x24): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `dm_pci_read_bar32'

This is because reference to dm_pci_read_bar32() remains in lib/fdtdec.c
while SPL build does not descend into drivers/pci directory in
drivers/Makefile if CONFIG_SPL_PCI_SUPPORT is not enabled.

Fix this by applying appropriate #define guards in lib/fdtdec.c.
It looks like ns16550.c has the same problem, so fixed that too.

To simplify this, CONFIG_SPL_PCI_SUPPORT is renamed to CONFIG_SPL_PCI
(enables use of CONFIG_IS_ENABLED() macro).

Suggested-by: Vignesh R <vigneshr@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/serial/ns16550.c b/drivers/serial/ns16550.c
index f3bd8db..560ca2a 100644
--- a/drivers/serial/ns16550.c
+++ b/drivers/serial/ns16550.c
@@ -425,7 +425,7 @@
 
 	/* try Processor Local Bus device first */
 	addr = dev_read_addr(dev);
-#if defined(CONFIG_PCI) && defined(CONFIG_DM_PCI)
+#if CONFIG_IS_ENABLED(PCI) && defined(CONFIG_DM_PCI)
 	if (addr == FDT_ADDR_T_NONE) {
 		/* then try pci device */
 		struct fdt_pci_addr pci_addr;