target/arm/cpu-features: Include missing 'cpu.h' header

target/arm/cpu-features: Include missing 'cpu.h' header

"target/arm/cpu-features.h" dereferences the ARMISARegisters
structure, which is defined in "cpu.h". Include the latter to
avoid when refactoring unrelated headers:

  In file included from target/arm/internals.h:33:
  target/arm/cpu-features.h:45:54: error: unknown type name 'ARMISARegisters'
     45 | static inline bool isar_feature_aa32_thumb_div(const ARMISARegisters *id)
        |                                                      ^
  target/arm/cpu-features.h:47:12: error: use of undeclared identifier 'R_ID_ISAR0_DIVIDE_SHIFT'
     47 |     return FIELD_EX32(id->id_isar0, ID_ISAR0, DIVIDE) != 0;
        |            ^

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-id: 20250513173928.77376-7-philmd@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>