MFC r300861,r300862:

r300861:

- Sort make variables
- Use SRCTOP instead of ad hoc definition for it

r300862:

Install ioatcontrol to /usr/bin by default instead of /

MFC r300856,r300857,r300858,r300874:

r300856:

Initialize `t` with memset(.., 0, ..)

This will help ensure that we're not using random garbage on the stack by
accident with respect to the variable

r300857:

Document the default behavior for -c (0)

Bump .Dd for the change

r300858:

Fix description for -V in the -r case

t.verify_test = true is always set when -V is specified, regardless of whether
or not the tool is being run in raw mode

r300874:

Update usage(..)

- Document missing options
- Sync options with ioatcontrol(8).
- Make it clear that the first 2 parameters are always required.

Fix build on stable/10.

MFC ioat(4) driver in its present state.