A11y - Focus on customize lock screen button

When activated. Talkback makes it clear to the user that
long-pressing on the lockscreen should activate the customize
lock screen button. Set focus to this element.

Fixes: 318028938
Test: manual - use talkback to activate customize lock screen
Flag: EXEMPT bugfix
Change-Id: I4b3e09127b66889bf62b55beee157aa8f14b03c0