soc/intel: Move pmc_soc_set_afterg3_en() to pmutil.c

soc/intel: Move pmc_soc_set_afterg3_en() to pmutil.c

Commit 2c26108208e4aa48de21be576ab6cad9286d7934 moved this function to
pmutil.c for Tiger Lake. Do this to all other platforms for consistency.
For Skylake, __SIMPLE_DEVICE__ preprocessor guards are no longer needed.

With this change, pmc.c is only needed in ramstage. Adjust Makefile.inc
accordingly, and drop ENV_RAMSTAGE guards from Skylake.

Change-Id: I424eb359c898f155659d085b888410b6bb58b9ed
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/52464
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Michael Niewöhner <foss@mniewoehner.de>