OpenBLAS

Use systemcfg APIs for CPU detection on AIX

AIX libc already provides ready access to an integer that contains a bit
identifying the CPU it's running on, so there's no need to call a
program and grep its output. Additionally, prtconf is not available in
the PASE runtime, which provides an AIX emulation layer on the IBM i
operating system.

The AIX systemcfg.h also provides macro definitions like POWER_8,
POWER_9, etc for all the bits defining the CPUs as well as macros like
__power_8(), __power_9_andup() that return booleans, but I did not use
them. Since these macros depend on the level of the OS in which it is
built, they may not be defined and instead the associated hex literals
are used directly.