clk: imx: gate4: Switch imx_clk_gate4_flags() to clk_hw based API

Switch the imx_clk_gate4_flags() function to clk_hw based API, rename
accordingly and add a macro for clk based legacy. This allows us to
move closer to a clear split between consumer and provider clk APIs.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Abel Vesa <abel.vesa@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>