ARM: div64: improve __arch_xprod_64()

Let's use the same criteria for overflow handling necessity as the
generic code.

Signed-off-by: Nicolas Pitre <[e-mail]>
Signed-off-by: Arnd Bergmann <[e-mail]>

arch/arm/include/asm/div64.h

···
 {
 	unsigned long long res;
 	register unsigned int tmp asm("ip") = 0;
+	bool no_ovf = __builtin_constant_p(m) &&
+		      ((m >> 32) + (m & 0xffffffff) < 0x100000000);
 
 	if (!bias) {
 		asm (	"umull	%Q0, %R0, %Q1, %Q2\n\t"
···
 			: "=&r" (res)
 			: "r" (m), "r" (n)
 			: "cc");
-	} else if (!(m & ((1ULL << 63) | (1ULL << 31)))) {
+	} else if (no_ovf) {
 		res = m;
 		asm (	"umlal	%Q0, %R0, %Q1, %Q2\n\t"
 			"mov	%Q0, #0"
···
 			: "cc");
 	}
 
-	if (!(m & ((1ULL << 63) | (1ULL << 31)))) {
+	if (no_ovf) {
 		asm (	"umlal	%R0, %Q0, %R1, %Q2\n\t"
 			"umlal	%R0, %Q0, %Q1, %R2\n\t"
 			"mov	%R0, #0\n\t"