clk: stm32mp1: Introduce STM32MP1 clock driver

This patch introduces the mechanism to probe stm32mp1 driver.
It also defines registers definition.
This patch also introduces the generic mechanism to register
a clock (a simple gate, divider and fixed factor).

All clocks will be defined in one table.

Signed-off-by: Gabriel Fernandez <gabriel.fernandez@st.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>