powerpc/44x: The bug fixed support for APM821xx SoC and Bluestone board

This patch consists of:
- Fix the pvr mask for checking pvr in cputable.c
- Fix the cpu name as consistent with cpu name is describled in dts file

Signed-off-by: Vinh Nguyen Huu Tuong <vhtnguyen@apm.com>
Signed-off-by: Josh Boyer <jwboyer@gmail.com>