target/sparc: convert to DisasContextBase

target/sparc: convert to DisasContextBase

Notes:

- pc and npc are left unmodified, since they can point to out-of-TB
  jump targets.

- Got rid of last_pc in gen_intermediate_code(), using base.pc_next
  instead. Only update pc_next (1) on a breakpoint (so that tb->size
  includes the insn), and (2) after reading the current instruction
  from memory. This allows us to use base.pc_next in the BP check,
  which is what the translator loop does.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Cc: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Cc: Artyom Tarasenko <atar4qemu@gmail.com>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>