First I2C implementation

Initial I2C HAL implementation.
Only the I2cMaster was tested so far, I2cSlave will be tested next.

Master side was tested with a temerature sensor example application
in the vorago-reb1 crate

src/lib.rs

@@ -5,6 +5,7 @@ pub use va108xx as pac;
 
 pub mod clock;
 pub mod gpio;
+pub mod i2c;
 pub mod prelude;
 pub mod spi;
 pub mod time;