Make arguments for booke_init() u_long, to match register width.

Make arguments for booke_init() u_long, to match register width.

On powerpc64, pointers are 64 bits, so casting from uint32_t changes the integer
width.

The alternative was to use register_t, but I didn't see register_t used as
argument type for any other functions, though didn't look too closely.  u_long
was an acceptable alternative.  On 64-bit it's 64 bits, on 32-bit it's 32 bits.