powerpc/64: Avoid isync in flush_dcache_range()

As per ISA an isync is only needed on instruction cache block
invalidate. Remove the same from dcache invalidate.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200320103242.229223-1-aneesh.kumar@linux.ibm.com

arch/powerpc/include/asm/cacheflush.h

@@ -65,17 +65,13 @@ static inline void flush_dcache_range(unsigned long start, unsigned long stop)
 	unsigned long size = stop - (unsigned long)addr + (bytes - 1);
 	unsigned long i;
 
-	if (IS_ENABLED(CONFIG_PPC64)) {
+	if (IS_ENABLED(CONFIG_PPC64))
 		mb();	/* sync */
-		isync();
-	}
 
 	for (i = 0; i < size >> shift; i++, addr += bytes)
 		dcbf(addr);
 	mb();	/* sync */
 
-	if (IS_ENABLED(CONFIG_PPC64))
-		isync();
 }
 
 /*