rockchip: timer: make register sizes explicit

We are about to reuse the rockchip timer (header file) for 64bit ARMv8
chips, so it seems a good time to make the register sizes explicit by
changing from 'unsigned int' to 'u32'.

Reorders the header-includes in rk_timer.c to ensure that 'u32' is
definded before it is used by 'asm/arch/timer.h'.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>