ANDROID: 16K: Fixup padding vm_flags bits on VMA splits

In some cases VMAs are split without the mmap write lock held;
later the lock is taken to fixup vm_flags of the original VMA.
Since some uppper bits of vm_flags are used to encode the ELF
padding ranges, they need to be modified on splits. This is
usually handled correctly by __split_vma(). However in the above
case, the flags get over witten later under the write lock.

Preserve vm_flag bits on reset to correctly represent padding.

Bug: 357901498
Change-Id: I1cb75419e614791a47cbdb0341373f619daf0bf2
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>