arm: socfpga: arria10: Enable cache driver in SPL

Adding "u-boot,dm-pre-reloc" and enable CONFIG_SPL_CACHE
to enable cache driver in SPL.

This fixed error below in SPL:
cache controller driver NOT found!

Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>
diff --git a/arch/arm/dts/socfpga_arria10-u-boot.dtsi b/arch/arm/dts/socfpga_arria10-u-boot.dtsi
index 0db358c..6ff1ea6 100644
--- a/arch/arm/dts/socfpga_arria10-u-boot.dtsi
+++ b/arch/arm/dts/socfpga_arria10-u-boot.dtsi
@@ -73,6 +73,10 @@
 	reset-names = "i2c";
 };
 
+&L2 {
+	u-boot,dm-pre-reloc;
+};
+
 &l4_mp_clk {
 	u-boot,dm-pre-reloc;
 };
diff --git a/arch/arm/mach-socfpga/Kconfig b/arch/arm/mach-socfpga/Kconfig
index 38d6c1b..a3699e8 100644
--- a/arch/arm/mach-socfpga/Kconfig
+++ b/arch/arm/mach-socfpga/Kconfig
@@ -46,6 +46,7 @@
 	bool
 	select SPL_ALTERA_SDRAM
 	select SPL_BOARD_INIT if SPL
+	select SPL_CACHE if SPL
 	select CLK
 	select SPL_CLK if SPL
 	select DM_I2C