[Bugfix] Add half type support in reshape_and_cache_cpu_impl on x86 cpu platform (#18430)

Signed-off-by: Yuqi Zhang <yuqizhang@google.com>
Co-authored-by: Yuqi Zhang <yuqizhang@google.com>

csrc/cpu/cpu_types_x86.hpp

@@ -19,6 +19,7 @@ namespace vec_op {
 #define VLLM_DISPATCH_CASE_FLOATING_TYPES_FP8(...)        \
   AT_DISPATCH_CASE(at::ScalarType::Float, __VA_ARGS__)    \
   AT_DISPATCH_CASE(at::ScalarType::BFloat16, __VA_ARGS__) \
+  AT_DISPATCH_CASE(at::ScalarType::Half, __VA_ARGS__)     \
   AT_DISPATCH_CASE(at::ScalarType::Float8_e5m2, __VA_ARGS__)
 
 #define VLLM_DISPATCH_FLOATING_TYPES(TYPE, NAME, ...) \