arm: Fix clang compilation for ARMv7

clang is not recognizing some pre-UAL VFP mnemonics like fnmacs, fnmacd,
fnmuls and fnmuld. Replaced them with equivalent UAL mnemonics which are
vmls.f32, vmls.f64, vnmul.f32 and vnmul.f64 respectively.

Optimise loads on Power9 LE

Since softfp code has been added to all required vfp kernels,
the code for auto detection of abi is no longer required.

The option to force softfp ABI on make command line by giving
ARM_SOFTFP_ABI=1 is retained. But there is no need to give this option
anymore.

Also the newly added C versions of 4x4/4x2 gemm/trmm kernels are removed.
These are longer required. Moreover these kernels has bugs.

In case of softfp abi, assembly implementations of only those APIs are
used which doesnt have a floating point argument or return value.

In case of hard abi, all assembly implementations are used.

Added generic 4x4 and 4x2 gemm kernels
Added generic 4x2 trmm kernel

Use lxvd2x instruction instead of lxvw4x.
lxvd2x performs far better on the new POWER architecture than lxvw4x.

Use lxvd2x instruction instead of lxvw4x.
lxvd2x performs far better on the new POWER architecture than lxvw4x.

Use lxvd2x instruction instead of lxvw4x.
lxvd2x performs far better on the new POWER architecture than lxvw4x.

Use lxvd2x instruction instead of lxvw4x.
lxvd2x performs far better on the new POWER architecture than lxvw4x.

Use lxvd2x instruction instead of lxvw4x.
lxvd2x performs far better on the new POWER architecture than lxvw4x.

Use lxvd2x instruction instead of lxvw4x.
lxvd2x performs far better on the new POWER architecture than lxvw4x.

Use lxvd2x instruction instead of lxvw4x.
lxvd2x performs far better on the new POWER architecture than lxvw4x.

Use lxvd2x instruction instead of lxvw4x.
lxvd2x performs far better on the new POWER architecture than lxvw4x.

Use lxvd2x instruction instead of lxvw4x.
lxvd2x performs far better on the new POWER architecture than lxvw4x.

Further fixes on top of 9e2f316ed.  Writing some doco for gcc on
inline assembly woke me up to some more errors.

- dgemv_kernel_4x4 asm did not mention *ap as a memory input, and
  *y is both read and write.
- sasum_kernel_32 and casum_kernel_16 did not use %x for a vsx insn
  operand, a problem if the "=f" sum output was ever allocated a vsx
  reg in the altivec set.  This might be possible with inlining and
  future gcc optimisation.

Blas 3 for single precision

make ARM_SOFTFP_ABI=1

Conventional usage of the register save area.

Optimized Implementations for ThunderX2T99

remove input from clobbered list