gen6_hiz: Don't bind GL_DRAW_FRAMEBUFFER on GLES

gen6_hiz: Don't bind GL_DRAW_FRAMEBUFFER on GLES

When using Mesa with a GLES API, calling _mesa_FramebufferRenderbuffer
with GL_DRAW_FRAMEBUFFER will report a 'user error' because
get_framebuffer_target validates that this enum from the framebuffer
blit extension is only used on GL. To work around it this patch makes
it use the GL_FRAMEBUFFER enum instead in that case.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=43418
Note: This is a candidate for the 8.0 branch.
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>