ARM HDLCD: Fix clock initialisation sequence

ARM HDLCD: Fix clock initialisation sequence

This reworks HDLCD initialisation to mirror how CLCD does this, in
particular to prepare the clock immediately after it has been got which
ensures that we don't try and enable clocks before they were prepared,
e.g. in the former clk_enable after register_framebuffer().

The reason this issue wasn't noticed before is that we have been
setting CONFIG_FRAMEBUFFER_CONSOLE and this caused
register_framebuffer() to trigger the creation of a console which calls
hdlcd_set_par(), which in turn was preparing and enabling the clock.

Signed-off-by: Jon Medhurst <tixy@linaro.org>