ACPICA: Debugger: refactor to fix unused variable warning

When building ACPICA in the Linux kernel with Clang with ACPI_DISASSEMBLER
not defined, we get a the following warning on variable display_op:

warning: variable 'display_op' set but not used [-Wunused-but-set-variable]

Fix this by refactoring display_op and parent_op code in a separate function.

Suggested-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Erik Schmauss <erik.schmauss@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>