Fix bug and re-enable vpx_int_pro_row/col_neon

Fix bug and re-enable vpx_int_pro_row/col_neon

Fix a bug in vpx_int_pro_row_neon (increment pointer after peeled
first loop iteration) and re-enable both vpx_int_pro_row/col_neon
paths.

Also fix IntProRowTest to use width_ (instead of 0) as the src_stride
for the input data block. The test's use of 0 for src_stride is the
reason the tests passed with the buggy Neon implementation noted in
the listed bugs. (The old buggy Neon implementation fails the
adjusted unit tests.)

BUG=webm:1800
BUG=webm:1809

Change-Id: I1f4572ee155653a7596fe2c10b5938ea7a3f63ae