arm: fix build with gcc 7

The compiler dislikes duplicat "const", and the ones it complains about
look like they we in fact meant to be placed differently.

Also fix array_access_okay() (just like on x86), despite the construct
being unused on ARM: -Wint-in-bool-context, enabled by default in
gcc 7, doesn't like multiplication in conditional operators. "Hide" it,
at the risk of the next compiler version becoming smarter and
recognizing even that. (The hope is that added smartness then would
also better deal with legitimate cases like the one here.) The change
could have been done in access_ok(), but I think we better keep it at
the place the compiler is actually unhappy about.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Note: Build tested only.

--- a/xen/arch/arm/platforms/brcm.c
+++ b/xen/arch/arm/platforms/brcm.c
@@ -271,7 +271,7 @@ static __init int brcm_init(void)
     return brcm_populate_plat_regs();
 }
 
-static const char const *brcm_dt_compat[] __initconst =
+static const char *const brcm_dt_compat[] __initconst =
 {
     "brcm,bcm7445d0",
     NULL
--- a/xen/arch/arm/platforms/rcar2.c
+++ b/xen/arch/arm/platforms/rcar2.c
@@ -46,7 +46,7 @@ static int __init rcar2_smp_init(void)
     return 0;
 }
 
-static const char const *rcar2_dt_compat[] __initdata =
+static const char *const rcar2_dt_compat[] __initconst =
 {
     "renesas,lager",
     NULL
--- a/xen/include/asm-arm/guest_access.h
+++ b/xen/include/asm-arm/guest_access.h
@@ -8,7 +8,8 @@
 #define access_ok(addr,size) (1)
 
 #define array_access_ok(addr,count,size) \
-    (likely(count < (~0UL/size)) && access_ok(addr,count*size))
+    (likely((count) < (~0UL / (size))) && \
+     access_ok(addr, 0 + (count) * (size)))
 
 unsigned long raw_copy_to_guest(void *to, const void *from, unsigned len);
 unsigned long raw_copy_to_guest_flush_dcache(void *to, const void *from,