[ARM] Add PM_LEGACY defaults

Eliminate two warnings:

kernel/power/pm.c:205: warning: 'pm_register' is deprecated (declared at kernel/power/pm.c:64)
kernel/power/pm.c:206: warning: 'pm_send_all' is deprecated (declared at kernel/power/pm.c:180)

by updating defconfig files to contain a sensible PM_LEGACY default.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>