sh: Enable skipping of bss on debug platforms for sh32 also.

This enables the same functionality that sh64 has for sh32. When running
on simulated hardware or via remote memory via the debug interface,
memory is gauranteed to be zero on boot already, and skipping the zeroing
of BSS has measurable boot time benefits.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>