libavcodec/ppc: Fix HEVC AltiVec routines with --enable-small

GCC requires the argument to vec_splat_u32 to be a literal.  The easiest
way to accomplish this is to change 'shift' to be const in scale (as it
is in the transform routine above), and convert both routines to be
inline.  This way, GCC can coerce the values to literals.

Tested on a 970 (Apple G5) and POWER9 (Talos II); passed fate and played
a clip of Big Buck Bunny correctly.

Fixes ticket #7048
Signed-off-by: A. Wilcox <AWilcox@Wilcox-Tech.com>

libavcodec/ppc/hevcdsp.c

@@ -41,8 +41,9 @@ static const vec_u8 mask[2] = {
     { 0x04, 0x05, 0x0C, 0x0D, 0x14, 0x15, 0x1C, 0x1D, 0x06, 0x07, 0x0E, 0x0F, 0x16, 0x17, 0x1E, 0x1F },
 };
 
-static void transform4x4(vec_s16 src_01, vec_s16 src_23, vec_s32 res[4],
-                         const int shift, int16_t *coeffs)
+static av_always_inline void transform4x4(vec_s16 src_01, vec_s16 src_23,
+                                          vec_s32 res[4], const int shift,
+                                          int16_t *coeffs)
 {
     vec_s16 src_02, src_13;
     vec_s32 zero = vec_splat_s32(0);
@@ -67,7 +68,8 @@ static void transform4x4(vec_s16 src_01, vec_s16 src_23, vec_s32 res[4],
     res[3] = vec_sub(e0, o0);
 }
 
-static void scale(vec_s32 res[4], vec_s16 res_packed[2], int shift)
+static av_always_inline void scale(vec_s32 res[4], vec_s16 res_packed[2],
+                                   const int shift)
 {
     int i;
     vec_u32 v_shift = vec_splat_u32(shift);