hw/tricore/triboard: Remove unnecessary use of &first_cpu

hw/tricore/triboard: Remove unnecessary use of &first_cpu

triboard_machine_init() has access to the single CPU via:

  TriBoardMachineState {
    TC27XSoCState {
      TriCoreCPU cpu;
      ...
    } tc27x_soc;
  } ms;

Pass it as argument to tricore_load_kernel() so we can
remove the &first_cpu global use.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Reviewed-by: Bastian Koppelmann <kbastian@mail.uni-paderborn.de>
Message-Id: <20250110180909.83165-1-philmd@linaro.org>