Put kernel_stats back into arch.

Put kernel_stats back into arch.

--HG--
rename : src/kern/alpha/idle_event.cc => src/arch/alpha/idle_event.cc
rename : src/kern/alpha/idle_event.hh => src/arch/alpha/idle_event.hh
rename : src/kern/alpha/kernel_stats.cc => src/arch/alpha/kernel_stats.cc
rename : src/kern/alpha/kernel_stats.hh => src/arch/alpha/kernel_stats.hh
rename : src/kern/sparc/kernel_stats.hh => src/arch/sparc/kernel_stats.hh
rename : src/kern/base_kernel_stats.cc => src/kern/kernel_stats.cc
rename : src/kern/base_kernel_stats.hh => src/kern/kernel_stats.hh
extra : convert_revision : 42bd3e36b407edbd19b912c9218f4e5923a15966