rockchip: update ROCKCHIP_SPL_RESERVE_IRAM to 0

Only rk3399 atf need ROCKCHIP_SPL_RESERVE_IRAM. This commit updates
its default setting to 0 so that other SoCs do not need to define it.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
diff --git a/arch/arm/mach-rockchip/Kconfig b/arch/arm/mach-rockchip/Kconfig
index 1e74db3..967290f 100644
--- a/arch/arm/mach-rockchip/Kconfig
+++ b/arch/arm/mach-rockchip/Kconfig
@@ -179,7 +179,7 @@
 
 config ROCKCHIP_SPL_RESERVE_IRAM
 	hex "Size of IRAM reserved in SPL"
-	default 0x4000
+	default 0
 	help
 	  SPL may need reserve memory for firmware loaded by SPL, whose load
 	  address is in IRAM and may overlay with SPL text area if not