powerpc/mpc85xx:Disable Debug TLB entry before init_tlbs

init_tlbs() initialize all the TLB entries required for the system.

So disable DEBUG TLB entry before TLB entries initialization.

Signed-off-by: Prabhakar Kushwaha <prabhakar@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>