i965: Rename some PIPE_CONTROL flags

i965: Rename some PIPE_CONTROL flags

I'm not really sure of the origins of the existing flag names. Modern docs have
some slightly different names. Having the correct names makes it easier to
determine if existing PIPE_CONTROL flag settings are correct, as well as making
adding new PIPE_CONTROLs easier.

This originally came up while I was trying to implement workarounds and spotted
some things called, "flush" which should have been called "invalidate."

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>