i965: Combine intel_batchbuffer_reloc and intel_batchbuffer_reloc64

i965: Combine intel_batchbuffer_reloc and intel_batchbuffer_reloc64

These two functions do the exact same thing.  One returns a uint64_t,
and the other takes the same uint64_t and truncates it to a uint32_t.

We only need the uint64_t variant - the caller can truncate if it wants.
This patch gives us one function, intel_batchbuffer_reloc, that does
the 64-bit thing.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>