[arch][arm] Don't read cbar register if cpu is not cortex-a9
[arch][arm] Don't read cbar register if cpu is not cortex-a9

It is not needed, and the register may not be available.

Change-Id: Ie09d4bba23820c552ccbf958856b231c9a526413

sndnvaps/lk,littlekernel/lk,minglun-tsai/lk,GCrean/lk,nvll/lk,srodrig1/lk,skabet/lk,grub4android/lk,hollanderic/lkstuff,hollanderic/lkstuff,ErikCorryGoogle/lk,ErikCorryGoogle/lk,srodrig1/lk,nvll/lk,ErikCorryGoogle/lk,GCrean/lk,nvll/lk,nvll/lk,grub4android/lk,skabet/lk,travisg/lk,hollanderic/lkstuff,sndnvaps/lk,hollanderic/lkstuff,srodrig1/lk,skabet/lk,ErikCorryGoogle/lk,GCrean/lk,littlekernel/lk,minglun-tsai/lk,travisg/lk,GCrean/lk,sndnvaps/lk,srodrig1/lk,travisg/lk,skabet/lk,grub4android/lk,minglun-tsai/lk,GCrean/lk,sndnvaps/lk,sndnvaps/lk,travisg/lk,minglun-tsai/lk,grub4android/lk,grub4android/lk,skabet/lk,littlekernel/lk,srodrig1/lk,nvll/lk,littlekernel/lk