target/sparc: Make sparc_cpu_tlb_fill sysemu only

target/sparc: Make sparc_cpu_tlb_fill sysemu only

The fallback code in cpu_loop_exit_sigsegv is sufficient
for sparc linux-user.

This makes all of the code in mmu_helper.c sysemu only, so remove
the ifdefs and move the file to sparc_softmmu_ss.  Remove the code
from cpu_loop that handled TT_DFAULT and TT_TFAULT.

Cc: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>