linux: Add support for pca9685 i2c pwm devices

Add support for controlling pca9685 PWM drivers using the standard
Linux I2C interface.  The pca9685 device is found on Replicape boards.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/linux/internal.h

@@ -5,6 +5,8 @@
 #include <time.h> // struct timespec
 
 // console.c
+void report_errno(char *where, int rc);
+int set_non_blocking(int fd);
 int console_setup(char *name);
 void console_sleep(struct timespec ts);