powerpc/8xx: Force VIRT_IMMR_BASE to be a positive number

The asm-offsets mechanism generates signed numbers, even if the
input value is explicitly unsigned.  This causes a problem with
older binutils (e.g. 2.23), which sign-extend a negative number
when @h is applied.  Thus, this instruction:

	cmpli   cr0, r11, VIRT_IMMR_BASE@h

resulted in this:

Error: operand out of range (0xfffffff0 is not between 0x00000000 and
0x0000ffff)

By casting to a larger type, we can force the output to be expressed
as a positive number.
Signed-off-by: Scott Wood <oss@buserror.net>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>

arch/powerpc/kernel/asm-offsets.c

@@ -754,7 +754,7 @@ int main(void)
 	DEFINE(PPC_DBELL_SERVER, PPC_DBELL_SERVER);
 
 #ifdef CONFIG_PPC_8xx
-	DEFINE(VIRT_IMMR_BASE, __fix_to_virt(FIX_IMMR_BASE));
+	DEFINE(VIRT_IMMR_BASE, (u64)__fix_to_virt(FIX_IMMR_BASE));
 #endif
 
 	return 0;