cpu: Directly use get_paging_enabled() fallback handlers in place

cpu: Directly use get_paging_enabled() fallback handlers in place

No code uses CPUClass::get_paging_enabled() outside of hw/core/cpu.c:

  $ git grep -F -- '->get_paging_enabled'
  hw/core/cpu.c:74:    return cc->get_paging_enabled(cpu);
  hw/core/cpu.c:438:    k->get_paging_enabled = cpu_common_get_paging_enabled;
  target/i386/cpu.c:7418:    cc->get_paging_enabled = x86_cpu_get_paging_enabled;

Check the handler presence in place and remove the common fallback code.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210517105140.1062037-10-f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>