MIPS: BCM63XX: merge bcm63xx_clk.h into bcm63xx/clk.c

All the header file does is provide the internal structure of clk,
which shouldn't be used by anyone except clk.c itself anyway.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Patchwork: http://patchwork.linux-mips.org/patch/5055/
Acked-by: John Crispin <blogic@openwrt.org>