Replace occurrences of arm64 with aarch64 in fragment and arch name.

Change-Id: I2c0a15e71e626c61c9e8151ef7365167d50b5d62
Reviewed-on: https://git.eclipse.org/r/c/platform/eclipse.platform.ui/+/179758
Tested-by: Lakshmi P Shanmugam <lshanmug@in.ibm.com>
Reviewed-by: Lakshmi P Shanmugam <lshanmug@in.ibm.com>