global: Rename SPL_ to XPL_

Use XPL_ as the symbol to indicate an SPL build. This means that SPL_ is
no-longer set.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/net/Makefile b/net/Makefile
index 64ab7ec..a1d3785 100644
--- a/net/Makefile
+++ b/net/Makefile
@@ -10,14 +10,14 @@
 obj-$(CONFIG_CMD_CDP)  += cdp.o
 obj-$(CONFIG_CMD_DNS)  += dns.o
 obj-$(CONFIG_DM_DSA)   += dsa-uclass.o
-obj-$(CONFIG_$(SPL_)DM_ETH) += eth-uclass.o
+obj-$(CONFIG_$(XPL_)DM_ETH) += eth-uclass.o
 obj-$(CONFIG_$(SPL_TPL_)BOOTDEV_ETH) += eth_bootdev.o
 obj-$(CONFIG_DM_MDIO)  += mdio-uclass.o
 obj-$(CONFIG_DM_MDIO_MUX) += mdio-mux-uclass.o
-obj-$(CONFIG_$(SPL_)DM_ETH) += eth_common.o
+obj-$(CONFIG_$(XPL_)DM_ETH) += eth_common.o
 obj-$(CONFIG_CMD_LINK_LOCAL) += link_local.o
 obj-$(CONFIG_IPV6)     += ndisc.o
-obj-$(CONFIG_$(SPL_)DM_ETH) += net.o
+obj-$(CONFIG_$(XPL_)DM_ETH) += net.o
 obj-$(CONFIG_IPV6)     += net6.o
 obj-$(CONFIG_CMD_NFS)  += nfs.o
 obj-$(CONFIG_CMD_PING) += ping.o