Make some inlined fns const.

The previous commit made a large number of functions const. Make the
function that we can const.

src/api/config/encoder.rs

@@ -186,7 +186,7 @@ impl EncoderConfig {
 
   /// Is temporal RDO enabled ?
   #[inline]
-  pub fn temporal_rdo(&self) -> bool {
+  pub const fn temporal_rdo(&self) -> bool {
     // Note: This function is called frequently, unlike most other functions here.
 
     // `compute_distortion_scale` computes a scaling factor for the distortion

src/asm/aarch64/dist.rs

@@ -59,7 +59,7 @@ declare_asm_dist_fn![
 const DIST_FNS_LENGTH: usize = 32;
 
 #[inline]
-fn to_index(bsize: BlockSize) -> usize {
+const fn to_index(bsize: BlockSize) -> usize {
   bsize as usize & (DIST_FNS_LENGTH - 1)
 }
 

src/asm/x86/dist/mod.rs

@@ -113,7 +113,7 @@ declare_asm_dist_fn![
 const DIST_FNS_LENGTH: usize = 32;
 
 #[inline]
-fn to_index(bsize: BlockSize) -> usize {
+const fn to_index(bsize: BlockSize) -> usize {
   bsize as usize & (DIST_FNS_LENGTH - 1)
 }
 

src/asm/x86/transform/forward.rs

@@ -65,13 +65,13 @@ struct I32X8 {
 impl I32X8 {
   #[target_feature(enable = "avx2")]
   #[inline]
-  unsafe fn vec(self) -> __m256i {
+  const unsafe fn vec(self) -> __m256i {
     self.data
   }
 
   #[target_feature(enable = "avx2")]
   #[inline]
-  unsafe fn new(a: __m256i) -> I32X8 {
+  const unsafe fn new(a: __m256i) -> I32X8 {
     I32X8 { data: a }
   }
 }

src/rdo.rs

@@ -558,7 +558,7 @@ impl From<DistortionScale> for f64 {
 
 impl RawDistortion {
   #[inline]
-  pub fn new(dist: u64) -> Self {
+  pub const fn new(dist: u64) -> Self {
     Self(dist)
   }
 }