imx233: always boost in bootloader

Many imx233 targets boot in a very low performance mode, typically cpu and
dram at 24MHz. This results in very slow boots and very unstable USB
bootloader mode. Since cpu frequency scaling is disabled in bootloader in
rockbox, always make the frequency scaling code available and boost at boot
time.

Change-Id: Ie96623c00f7c4cd9a377b84dcb14b772558cfa4d
3 files changed