ARM: l2c: fix dependencies on PL310 errata symbols

A number of configurations spit out warnings similar to:

warning: (SOC_IMX6 && SOC_VF610 && ARCH_OMAP4) selects PL310_ERRATA_588369 which has unmet direct dependencies (CACHE_L2X0)
warning: (SOC_IMX6 && SOC_VF610 && ARCH_OMAP4) selects PL310_ERRATA_727915 which has unmet direct dependencies (CACHE_L2X0)

Clean up the dependencies here:
* PL310 symbols should only be selected when CACHE_L2X0 is enabled.
* Since the cache-l2x0 code detects PL310 presence at runtime, and we will
  eventually get rid of CACHE_PL310, surround these errata options with an
  if CACHE_L2X0 conditional rather than repeating the dependency against
  each.

Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mach-vexpress/Kconfig

@@ -44,7 +44,7 @@ config ARCH_VEXPRESS_CORTEX_A5_A9_ERRATA
 	bool "Enable A5 and A9 only errata work-arounds"
 	default y
 	select ARM_ERRATA_720789
-	select PL310_ERRATA_753970 if CACHE_PL310
+	select PL310_ERRATA_753970 if CACHE_L2X0
 	help
 	  Provides common dependencies for Versatile Express platforms
 	  based on Cortex-A5 and Cortex-A9 processors. In order to