checkpatch: add --showfile to allow input via pipe to show filenames

checkpatch: add --showfile to allow input via pipe to show filenames

Using "git diff | ./scripts/checkpatch -" does not have an
easy mechanism to see the files and lines actually modified.

Add --showfile to see the file and line specified in the diff.

When --showfile is used without --terse, the second line of each
message output is redundant, so it is removed.

Signed-off-by: Joe Perches <[email protected]>
Cc: Petr Mladek <[email protected]>
Cc: Andy Whitcroft <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>