Convert CONFIG_SYS_L2_PL310 to Kconfig

This converts CONFIG_SYS_L2_PL310 to Kconfig.

For omap2 and mvebu the 'select SYS_L2_PL310' locations were
determined using ./tools/moveconfig -i CONFIG_SYS_L2_PL310.

For mx6 I manually chose ARCH_MX6 as 'select' location. The
correctness has been verified using

	$ ./tools/moveconfig.py -f ARCH_MX6 ~SYS_L2_PL310 ~SYS_L2CACHE_OFF
	0 matches

That means whenever an ARCH_MX6 board had SYS_L2_PL310 disabled, this
was correctly reflected in SYS_L2CACHE_OFF. Thus it's safe to insert
the 'select' statement under ARCH_MX6.

Signed-off-by: Philip Oberfichtner <pro@denx.de>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 0b72e4f..456a7fa 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -488,6 +488,10 @@
 	   density. For ARM architectures that support Thumb2 this flag will
 	   result in Thumb2 code generated by GCC.
 
+config SYS_L2_PL310
+	bool "ARM PL310 L2 cache controller"
+	help
+	  Enable support for ARM PL310 L2 cache controller in U-Boot
 
 config SYS_L2CACHE_OFF
 	bool "L2cache off"
@@ -989,6 +993,7 @@
 	select SYS_FSL_HAS_SEC
 	select SYS_FSL_SEC_COMPAT_4
 	select SYS_FSL_SEC_LE
+	select SYS_L2_PL310 if !SYS_L2CACHE_OFF
 	imply MXC_GPIO
 	imply SYS_THUMB_BUILD
 	imply SPL_SEPARATE_BSS