x86: acpi: Deduplicate acpi_fill_madt() implementation

In Baytrail and Quark support code acpi_fill_madt() is identical.

Deduplicate its implementation by moving to lib/acpi_tables.c.

At the same time mark acpi_fill_madt() with __weak attribute to keep a
possibility to override it in platform code

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>