clk: imx: add imx7ulp clk driver

clk: imx: add imx7ulp clk driver

i.MX7ULP Clock functions are under joint control of the System
Clock Generation (SCG) modules, Peripheral Clock Control (PCC)
modules, and Core Mode Controller (CMC)1 blocks

The clocking scheme provides clear separation between M4 domain
and A7 domain. Except for a few clock sources shared between two
domains, such as the System Oscillator clock, the Slow IRC (SIRC),
and and the Fast IRC clock (FIRCLK), clock sources and clock
management are separated and contained within each domain.

M4 clock management consists of SCG0, PCC0, PCC1, and CMC0 modules.
A7 clock management consists of SCG1, PCC2, PCC3, and CMC1 modules.

This driver only adds clock support in A7 domain.

Note that most clocks required to be operated when gated, e.g. pll,
pfd, pcc. And more special cases that scs/ddr/nic mux selecting
different clock source requires that clock to be enabled first,
then we need set CLK_OPS_PARENT_ENABLE flag for them properly.

Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Michael Turquette <mturquette@baylibre.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Anson Huang <Anson.Huang@nxp.com>
Cc: Bai Ping <ping.bai@nxp.com>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>