powerpc: P1010RDB: Rework local command to not be included in SPL

Add a CONFIG_SPL_BUILD guard around the code for the "mux" command so
it is not included in SPL.

Cc: Qiang Zhao <qiang.zhao@nxp.com>
Cc: York Sun <york.sun@nxp.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: York Sun <york.sun@nxp.com>
Reviewed-by: Qiang Zhao <qiang.zhao@nxp.com>

board/freescale/p1010rdb/p1010rdb.c

@@ -550,6 +550,7 @@ int misc_init_r(void)
 	return 0;
 }
 
+#ifndef CONFIG_SPL_BUILD
 static int pin_mux_cmd(cmd_tbl_t *cmdtp, int flag, int argc,
 				char * const argv[])
 {
@@ -569,3 +570,4 @@ U_BOOT_CMD(
 	"configure multiplexing pin for IFC/SDHC bus in runtime",
 	"bus_type (e.g. mux sdhc)"
 );
+#endif