x86: acpi: Update acpi_fill_csrt() to use acpi_ctx

x86: acpi: Update acpi_fill_csrt() to use acpi_ctx

Update this function to the newer style, so we can avoid passing and
returning an address through this function.

Also move this function out of the x86 code so it can be used by other
archs.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>