clk: sunxi: Move USB clocks to separate file

The USB clocks originally shared code with the gates clocks, but had
additional reset controllers. Move these to a separate file. This will
allow us to add new support for slightly different USB clocks, such as
on the A80, without affecting gates clocks, and also facilitate the
migration of gates clocks to a generic solution.

This also cleans up the USB clocks code slightly, such as adding
newlines, getting rid of the unused clkdev call, using a simple
u32 instead of BITMAP for the clock masks, using BIT() macro to
declare the clock bitmasks, and using of_io_request_and_map() to
get the I/O address.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>