Note that PowerPC has not dozens of extensions / features like x86. It is required to read specific privileged registers that may depend on cores.
I checked on Linux and you can access PVR, there is a trap in the kernel to manage that.
Reading /proc/cpuinfo can return if Altivec is supported, the memory and L2 cache size ... but that is not really convenient.
A better solution is described here: http://www.freehackers.org/thomas/2011/05/13/how-to-detect-altivec-availability-on-linuxppc-at-runtime/
That uses the content of /proc/self/auxv that provides "the ELF interpreter information passed to the process at exec time".
The example is about Altivec but you can get other features (listed in include "asm/cputable.h"): 32 or 64 bit cpu, Altivec, SPE, FPU, MMU, 4xx MAC, ...
Last, you will find information on caches (size, line size, associativity, ...), look at files in: /sys/devices/system/cpu/cpu0/cache