sparc: mv sparc sysctls into their own file under arch/sparc/kernel

sparc: mv sparc sysctls into their own file under arch/sparc/kernel

Move sparc sysctls (reboot-cmd, stop-a, scons-poweroff and tsb-ratio)
into a new file (arch/sparc/kernel/setup.c). This file will be included
for both 32 and 64 bit sparc. Leave "tsb-ratio" under SPARC64 ifdef as
it was in kernel/sysctl.c. The sysctl table register is called with
arch_initcall placing it after its original place in proc_root_init.

This is part of a greater effort to move ctl tables into their
respective subsystems which will reduce the merge conflicts in
kernel/sysctl.c.

Signed-off-by: Joel Granados <joel.granados@kernel.org>