Clock get parent EEMI API is reimplemented to use system-level clock
and pll EEMI APIs rather than direct MMIO read/write accesses to clock
and pll control registers.
Since linux still uses clock set parent API to get pre_src, post_src, div2
and bypasss, in the implementation of pm_clock_get_parent() we need to
workaround this by distinguishing two cases:
1) if the given clock ID corresponds to a PLL-related clock ID (*_PRE_SRC,
   *_POST_SRC, *_INT_MUX or *_PLL clock IDs); or
2) given clock ID is truly an on-chip clock.
For case 1) we'll map the call onto PLL-specific EEMI API with the
respective parameter ID. For case 2) the call is passed to the PMU.

Signed-off-by: Mirela Simonovic <mirela.simonovic@aggios.com>
Acked-by: Will Wong <WILLW@xilinx.com>
Signed-off-by: Jolly Shah <jollys@xilinx.com>