The Data Stream Control Register (DSCR) is privileged on POWER7, but
unprivileged (different register) on POWER8 and later. However, it's now
guarded by a new register, the Facility Status and Control Register, instead of
the MSR like other pre-existing facilities (FPU, Altivec). The FSCR must be
managed explicitly, since it's effectively an extension of the MSR.
Tested by: Brandon Bergren
a058a87622