avcodec/mips: Improve hevc uni-w copy mc msa functions

Load the specific destination bytes instead of MSA load and pack.
Pack the data to half word before clipping.
Use immediate unsigned saturation for clip to max saving one vector register.
Signed-off-by: Kaustubh Raste <kaustubh.raste@imgtec.com>
Reviewed-by: Manojkumar Bhosale <Manojkumar.Bhosale@imgtec.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavutil/mips/generic_macros_msa.h

@@ -204,6 +204,12 @@
     out3 = LW((psrc) + 3 * stride);                \
 }
 
+#define LW2(psrc, stride, out0, out1)  \
+{                                      \
+    out0 = LW((psrc));                 \
+    out1 = LW((psrc) + stride);        \
+}
+
 /* Description : Load double words with stride
    Arguments   : Inputs  - psrc    (source pointer to load from)
                          - stride
@@ -1047,6 +1053,25 @@
     CLIP_SH2_0_255(in2, in3);               \
 }
 
+#define CLIP_SH_0_255_MAX_SATU(in)                    \
+( {                                                   \
+    v8i16 out_m;                                      \
+                                                      \
+    out_m = __msa_maxi_s_h((v8i16) in, 0);            \
+    out_m = (v8i16) __msa_sat_u_h((v8u16) out_m, 7);  \
+    out_m;                                            \
+} )
+#define CLIP_SH2_0_255_MAX_SATU(in0, in1)  \
+{                                          \
+    in0 = CLIP_SH_0_255_MAX_SATU(in0);     \
+    in1 = CLIP_SH_0_255_MAX_SATU(in1);     \
+}
+#define CLIP_SH4_0_255_MAX_SATU(in0, in1, in2, in3)  \
+{                                                    \
+    CLIP_SH2_0_255_MAX_SATU(in0, in1);               \
+    CLIP_SH2_0_255_MAX_SATU(in2, in3);               \
+}
+
 /* Description : Clips all signed word elements of input vector
                  between 0 & 255
    Arguments   : Inputs  - in       (input vector)
@@ -1965,6 +1990,11 @@
                  result is in place written to 'in0'
                  Similar for other pairs
 */
+#define SLLI_2V(in0, in1, shift)  \
+{                                 \
+    in0 = in0 << shift;           \
+    in1 = in1 << shift;           \
+}
 #define SLLI_4V(in0, in1, in2, in3, shift)  \
 {                                           \
     in0 = in0 << shift;                     \