accel/kvm: Include missing 'exec/cpu-common.h' header

kvm-accel-ops.c uses EXCP_DEBUG, itself defined in
"exec/cpu-common.h". Include it explicitly, otherwise
we get when modifying unrelated headers:

  ../accel/kvm/kvm-accel-ops.c: In function ‘kvm_vcpu_thread_fn’:
  ../accel/kvm/kvm-accel-ops.c:54:22: error: ‘EXCP_DEBUG’ undeclared (first use in this function)
     54 |             if (r == EXCP_DEBUG) {
        |                      ^~~~~~~~~~

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20260225051303.91614-2-philmd@linaro.org>