ACPI / table: Add new function to get table entries

The acpi_table_parse() function has a callback that
passes a pointer to a table_header. Add a new function
which takes this pointer and parses its entries. This
eliminates the need to re-traverse all the tables for
each call. e.g. as in acpi_table_parse_madt() which is
normally called after acpi_table_parse().

Acked-by: Grant Likely <grant.likely@linaro.org>
Signed-off-by: Ashwin Chaugule <ashwin.chaugule@linaro.org>
Signed-off-by: Tomasz Nowicki <tomasz.nowicki@linaro.org>
Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>