[MachO] Give the CPUSubTypeARM64 enum uint32_t type. NFCI.
We recently added various CPU_SUBTYPE_ARM64E values, notably including
CPU_SUBTYPE_ARM64E_VERSIONED_PTRAUTH_ABI_MASK, which is 0x80000000U.
The enum is better off as a uint32_t to accomodate that.
This also hopefully helps silence GCC warnings reported on a ternary in
CPU_SUBTYPE_ARM64E_WITH_PTRAUTH_VERSION.
The subtype is already generally treated as a uint32_t elsewhere, so
while there, change the new helpers to explicitly pass/return the
subtype as uint32_t, and the individual narrower components as either
bool or unsigned.