cputlb: Partially merge tlb_dyn_init into tlb_init

cputlb: Partially merge tlb_dyn_init into tlb_init

Merge into the only caller, but at the same time split
out tlb_mmu_init to initialize a single tlb entry.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>