Reformat the copyright header of deblocking_neon.S

This makes it identical to the ones in the other files.
Remove a redundant definition of WELSEMMS

The same definition already exists in asm_inc.asm.
Avoid unnecessary tabs in macro declarations
Get rid of double spaces in macro declarations
Convert all tabs to spaces in assembly sources, unify indentation

Previously the assembly sources had mixed indentation consisting
of both spaces and tabs, making it quite hard to read unless
the right tab size was used in the editor.

Tabs have been interpreted as 4 spaces in most cases, matching
the surrounding code.
Merge pull request #911 from mstorsjo/reformat-asm

Convert all tabs to spaces in assembly sources, unify indentation