[Arm builtins] Remove non-necessary IS check

This patch removes the instruction set check to make the msr APSR_nzcvq,
ip instruction only execute if Thumb2 is used.
The APSR is a subset of the bits of the CPSR
(B.1.3.3 of the Arm v7 A and R ARM [1]) and is only available for A and
R profiles.
However in section B.9.3.11 of the same document we see that:

"In the A and R profiles, APSR_nzcvq is the same as CPSR_f"
"ARM recommends the APSR forms when only the N, Z, C, V, Q, and GE[3:0]
bits are being written."

This patch also make those files assemble for Armv8-M Mainline
architecture profile.

The builtins were cross-compiled for Arm, Aarch64 and Armv6-M, Armv7-M
and Armv7E-M targets.
Cross-compiled tests were executed for Arm target.

[1]: https://developer.arm.com/docs/ddi0406/latest/arm-architecture-reference-manual-armv7-a-and-armv7-r-edition

Patch by hug-dev (Hugues de Valon).

Differential Revision: https://reviews.llvm.org/D51854

llvm-svn: 343601