i2c: Add new I2C Slave syscalls

This patchs adds new I2C Syscalls for :
- I2C controllers slave support
- I2C Slave drivers support

I2C Controllers slave support adds 2 new ops to :
- register new slave driver
- unregister slave driver

Slave funcs consists on all the I2C phases :
- read or write request once address matches
- read or write done once the byte has been received/sent
- stop when the trasmit stops

I2C Slave drivers syscall are also added to make new
"I2C Slave" drivers to :
- register them to their I2C controller
- unregister them to their I2C controller

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>