ANDROID: 16K: Handle pad VMA splits and merges

In some cases a VMA with padding representation may be split, and
therefore the padding flags must be updated accordingly.

There are 3 cases to handle:

Given:
    | DDDDPPPP |

where:
    - D represents 1 page of data;
    - P represents 1 page of padding;
    - | represents the boundaries (start/end) of the VMA

1) Split exactly at the padding boundary

    | DDDDPPPP | --> | DDDD | PPPP |

    - Remove padding flags from the first VMA.
    - The second VMA is all padding

2) Split within the padding area

    | DDDDPPPP | --> | DDDDPP | PP |

    - Subtract the length of the second VMA from the first VMA's
      padding.
    - The second VMA is all padding, adjust its padding length (flags)

3) Split within the data area

    | DDDDPPPP | --> | DD | DDPPPP |

    - Remove padding flags from the first VMA.
    - The second VMA is has the same padding as from before the split.

To simplify the semantics merging of padding VMAs is not allowed.

If a split produces a VMA that is entirely padding, show_[s]maps()
only outputs the padding VMA entry (as the data entry is of length 0).

Bug: 330117029
Bug: 327600007
Bug: 330767927
Bug: 328266487
Bug: 329803029
Change-Id: Ie2628ced5512e2c7f8af25fabae1f38730c8bb1a
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>