Using the CMSIS macros _VAL2FLD(field, value) and _FLD2VAL(field, value) you can access bit fields more easily.
Code example
id = _FLD2VAL(SCB_CPUID_REVISION, SCB->CPUID); // uses the #define's _Pos and _Msk of the related bit field to extract the value of a bit field from a register.
SCB->CPUID = _VAL2FLD(SCB_CPUID_REVISION, 0x3) | _VAL2FLD(SCB_CPUID_VARIANT, 0x3); // uses the #define's _Pos and _Msk of the related bit field to shift bit-field values for assigning to a register.