ARM: davinci: serial: provide API to initialze UART clocks

Provide an API to initialize a UART clock. Refactor existing
davinci_serial_init() to separate out the part which enables
the clock.

This will later be used to help DA850 DT boot support.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>

arch/arm/mach-davinci/include/mach/serial.h

@@ -43,6 +43,7 @@ struct davinci_uart_config {
 };
 
 extern int davinci_serial_init(struct davinci_uart_config *);
+extern int davinci_serial_setup_clk(unsigned instance, unsigned int *rate);
 #endif
 
 #endif /* __ASM_ARCH_SERIAL_H */