anv: Stop setting BO flags in bo_init_new

anv: Stop setting BO flags in bo_init_new

The idea behind doing this was to make it easier to set various flags.
However, we have enough custom flag settings floating around the driver
that this is more of a nuisance than a help.  This commit has the
following functional changes:

 1) The workaround_bo created in anv_CreateDevice loses both flags.
    This shouldn't matter because it's very small and entirely internal
    to the driver.

 2) The bo created in anv_CreateDmaBufImageINTEL loses the
    EXEC_OBJECT_ASYNC flag.  In retrospect, it never should have gotten
    EXEC_OBJECT_ASYNC in the first place.

Reviewed-by: Nanley Chery <nanley.g.chery@intel.com>
Cc: "17.1" <mesa-stable@lists.freedesktop.org>