cpufreq/amd-pstate: Replace all AMD_CPPC_* macros with masks

Bitfield masks are easier to follow and less error prone.

Reviewed-by: Dhananjay Ugwekar <dhananjay.ugwekar@amd.com>
Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>