soc/intel/common: Refine pmc_get_xtal_freq function

1. Remove 'PCH_EPOC_XTAL_FREQ(__epoc)' macro since it only be used
   in 1 place.

2. Transform macro into more readable C code.

3. Add additional case check to make sure the returned value is
   defined in the 'pch_pmc_xtal' enum.

Signed-off-by: Lean Sheng Tan <lean.sheng.tan@intel.com>
Change-Id: If57a99bf8e837a6eb8f225297399b1f5363cfa85
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55587
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

0 files changed, 0 insertions, 0 deletions