i965/fs: Take # of components into account in try_rewrite_rhs_to_dst.

i965/fs: Take # of components into account in try_rewrite_rhs_to_dst.

Commit dc7f449d1ac53a66e6efb56ccf2a5953418a26ca introduced a new method
for avoiding MOVs: try to rewrite the destination of the instruction
that produced the RHS so it writes into the LHS.

Unfortunately, this is not safe for swizzled texturing operations, as
they return a set of four contiguous registers.  Consider the following:

(assign (x)
        (var_ref vec_ctor_x)
        (swiz x (tex vec4 (var_ref m_sampY) (var_ref m_cordY) 0 1 ())))

In this case, the source and destination registers are equal, since
reg_offset is 0 for both.  Yet, this is only a partial move: the texture
operation generates four registers, and the LHS only covers one.

Fixes color distortion in XBMC when using GLSL shaders.

NOTE: This is a candidate for the 8.0 branch (with the previous commit).

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=44333
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>