Re-land 634b0243b8.
T1 allow for an optional registers list,
the register list must be {d0-d15}.
T2 define a mandatory register list,
the register list must be {d0-d31}.
The requirements for T1/T2 are as follows:
T1 T2
Require: v8-M.Main, v8.1-M.Main,
secure state secure state
16 D Regs valid valid
32 D Regs UNDEFINED valid
No D Regs NOP NOP