powerpc/booke: Fix 32-bit Book-E SMP AP bringup

r354266 changed the type of bp_kernload to vm_paddr_t in platform_mpc85xx.c,
but not the variable itself in locore.S. This caused the AP to not come up,
due to overwriting the following variable (bp_virtaddr). Also, properly
load bp_kernload into MAS3 and MAS7. Prior to r354266, we required loading
into the low 4GB, but now we can load from anywhere in memory that ubldr can
access.