base-hw: fix bug in 'Platform_thread::pager()'

fix #644
base-hw & arm_v7: fix CPU initialization bug
hw_arndale: create builddir support
arndale: UART driver base
arndale: board driver base
cortex_a15: base/mk spec
arndale: base/mk platform spec
hw_arndale: enable nested init test
base-hw: rework 'run/env', enable '--target uboot'
base-hw: provide SIGNAL service in nested_init.run
base: make signal framework usable for base-hw
base-hw: destroy signal contexts, generic signal.h
timer & hw & omap4: compile bug in Platform_timer