clk: nuvoton: Add clk-ma35d1.h for driver extern functions

Moved the declaration of extern functions ma35d1_reg_clk_pll() and
ma35d1_reg_adc_clkdiv() from the .c files to the newly created header
file clk-ma35d1.h.

Signed-off-by: Jacky Huang <ychuang3@nuvoton.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>