ARM: davinci: only select WT cache if cache is enabled

The DA830 chip only works if the dcache is in writethrough mode, but that produces a harmless Kconfig warning if the cache happens to be disabled:

warning: (ARCH_DAVINCI_DA830) selects CPU_DCACHE_WRITETHROUGH which has unmet direct dependencies ((CPU_ARM740T || CPU_ARM920T || CPU_ARM922T || CPU_ARM925T || CPU_ARM926T || CPU_ARM940T || CPU_ARM946E || CPU_ARM1020 || CPU_FA526) && !CPU_DCACHE_DISABLE)

This makes the select conditional so we don't have to worry about the warning in randconfig builds any more.

---

index 88233824d1fe..83e0f40f9ff1 100644
@@ -34,7 +34,8 @@ config ARCH_DAVINCI_DA830
 	bool "DA830/OMAP-L137/AM17x based system"
 	depends on !ARCH_DAVINCI_DMx || AUTO_ZRELADDR
 	select ARCH_DAVINCI_DA8XX
-	select CPU_DCACHE_WRITETHROUGH # needed on silicon revs 1.0, 1.1
+	# needed on silicon revs 1.0, 1.1:
+	select CPU_DCACHE_WRITETHROUGH if !CPU_DCACHE_DISABLE
 	select CP_INTC
 
 config ARCH_DAVINCI_DA850

Applied.

Thanks,
Sekhar