s390/boot: Respect kaslr_enabled() for identity randomization

CONFIG_RANDOMIZE_IDENTITY_BASE only enables support for randomizing the
identity mapping base. The randomization (identity base != 0) itself
should happen only when KASLR is enabled at runtime.

Guard the __identity_base update with kaslr_enabled() so nokaslr (and
other KASLR-disabled cases) keep the non-randomized identity mapping at 0.

Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

Author: Vasily Gorbik

arch/s390/boot/startup.c

@@ -440,7 +440,8 @@ static unsigned long setup_kernel_memory_layout(unsigned long kernel_size)
 	max_mappable = max(ident_map_size, MAX_DCSS_ADDR);
 	max_mappable = min(max_mappable, vmemmap_start);
 #ifdef CONFIG_RANDOMIZE_IDENTITY_BASE
-	__identity_base = round_down(vmemmap_start - max_mappable, rte_size);
+	if (kaslr_enabled())
+		__identity_base = round_down(vmemmap_start - max_mappable, rte_size);
 #endif
 	boot_debug("identity map:        0x%016lx-0x%016lx\n", __identity_base,
 		   __identity_base + ident_map_size);