clk: mediatek: support COMMON_CLK_MT6779 module build

clk: mediatek: support COMMON_CLK_MT6779 module build

To support COMMON_CLK_MT6779* module build,
add MODULE_LICENSE and export necessary symbols.

Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Hanks Chen <hanks.chen@mediatek.com>
Cc: Wendell Lin <wendell.lin@mediatek.com>
Cc: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Miles Chen <miles.chen@mediatek.com>
Link: https://lore.kernel.org/r/20210901222526.31065-4-miles.chen@mediatek.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>