Refer initrd_start, initrd_end directly from drivers/acpi/tables.c.
This allows to use the table upgrade feature in architectures
other than x86.  Also this simplifies header files.

The patch renames acpi_table_initrd_init() to acpi_table_upgrade()
(what reflects the purpose of the function) and removes the unneeded
wraps early_acpi_table_init() and early_initrd_acpi_init().
Signed-off-by: NAleksey Makarov <aleksey.makarov@linaro.org>
Acked-by: NLv Zheng <lv.zheng@intel.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>