platform/x86: intel_telemetry: Add telemetry_get_pltdata()

Add new function that allows telemetry modules to get pointer to the
platform specific configuration. This is needed to allow the telemetry
debugfs module to fetch PMC IPC instance in the subsequent patch.

This also allows us to replace telemetry_pltconfig_valid() with
telemetry_get_pltdata() as well.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>