MCPWM group clock pre scale was originally fixed to 2, which is
inconvenient. Set group clock prescale dynamically. Now the maximum
resolution of the MCPWM timer is up to 160MHz(when the prescale set
to 1). And add a resulotion config for MCPWM capture.
The MCPWM carrier is part of the operator and can work independently
without the MCPWM timer being enabled. This commit add the MCPWM
carrier clk source.
