ACPI: debug: Make two functions static

Fix sparse warnings:

drivers/acpi/acpi_dbg.c:748:12: warning:
 symbol 'acpi_aml_init' was not declared. Should it be static?
drivers/acpi/acpi_dbg.c:774:13: warning:
 symbol 'acpi_aml_exit' was not declared. Should it be static?

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>