riscv: sifive/fu540: spl: Rename soc_spl_init()

spl_soc_init() seems to be a better name, as all SPL functions
names start from the spl_ prefix.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Rick Chen <rick@andestech.com>
Reviewed-by: Pragnesh Patel <pragnesh.patel@sifive.com>
Tested-by: Pragnesh Patel <pragnesh.patel@sifive.com>

board/sifive/fu540/spl.c

@@ -21,7 +21,7 @@ int spl_board_init_f(void)
 {
 	int ret;
 
-	ret = soc_spl_init();
+	ret = spl_soc_init();
 	if (ret) {
 		debug("FU540 SPL init failed: %d\n", ret);
 		return ret;