The current driver code gives the crash or gets hang while switching
the CPU frequency some time. The APSS CPU Clock divider is not glitch
free so it the APPS clock need to be switched for stable clock during
the change.

This patch adds the frequency change notifier for APSS CPU clock. It
changes the parent of this clock to stable PLL FEPLL500 for
PRE_RATE_CHANGE event. This event will be generated before actual
clock set operations. The clock set operation will again change its
corresponding parent by getting the same from frequency table.
Signed-off-by: Abhishek Sahu <absahu@codeaurora.org>
[sboyd@codeaurora.org: Indent less in probe]
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>