Make arch_idle and arch_reset inline as inline function.

Not having them inline leads to a warning of this sort when only
one of these functions is used:

arch/arm/mach-davinci/include/mach/system.h:24: warning: 'arch_reset' \
defined but not used

boot, re-boot tested on OMAP-L138 EVM
Signed-off-by: NSekhar Nori <nsekhar@ti.com>
Signed-off-by: NKevin Hilman <khilman@deeprootsystems.com>