ANDROID: 16K: Allocate pad vma on the stack

Now that the padding VMA is only used in show_map_pad_vma(),
initialize the padding VMA struct on the stack.

This is a nice clean up and avoid having to deal with dynamic
allocation failure.

Bug: 440210631
Bug: 432564748
Change-Id: I168cda6cdb98423a40bb691b687c0f99bd160db6
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>