platform/x86: intel_speed_select_if: Remove hardcoded map size

platform/x86: intel_speed_select_if: Remove hardcoded map size

The driver is using 256 as the size while calling devm_ioremap(). The
maximum offset can be obtained from isst_mmio_range. Add a field "size"
to the isst_mmio_range and use it instead of hardcoding.

No functional impact is expected.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20231003163234.1856669-4-srinivas.pandruvada@linux.intel.com
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>