ARM: use "* SZ_1M" rather than "<< 20"

Make the default vmalloc size clearer by using a more natural
multiplication by SZ_1M rather than a shift left by 20 bits.
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Yanfei Xu <yanfei.xu@windriver.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

arch/arm/mm/mmu.c

@@ -1121,7 +1121,7 @@ void __init debug_ll_io_init(void)
 }
 #endif
 
-static unsigned long __initdata vmalloc_size = 240 << 20;
+static unsigned long __initdata vmalloc_size = 240 * SZ_1M;
 
 /*
  * vmalloc=size forces the vmalloc area to be exactly 'size'