platform/x86: Drop the PMC_ATOM Kconfig option

The def_bool y PMC_ATOM Kconfig option provides a couple of symbols used
by the code enabled by the X86_INTEL_LPSS option and it registers some
clocks. These clocks are only registered on Bay Trail, Cherry Trail and
Brasswell Intel SoCs and kernels targeting these SoCs must always have
the X86_INTEL_LPSS option enabled otherwise many things will not work.

Building the PMC_ATOM code on kernels which are not targeting the
mentioned SoCs and which do not have the X86_INTEL_LPSS enabled is
not useful.

This means that we can simplify things by replacing the PMC_ATOM Kconfig
option in Makefiles with X86_INTEL_LPSS and then drop the option.

Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Acked-by: Stephen Boyd <sboyd@kernel.org>
Link: https://lore.kernel.org/r/20220503140207.101218-2-hdegoede@redhat.com