base-hw & arm: bugs when zero-filling BSS

fix #654
timer & hw & omap4: compile bug in Platform_timer

fix #652
base-codezero: initialize 'exregs_data' objects

Fixes #651.
base-hw: fix bug in 'Platform_thread::pager()'
base-hw & arm_v7: fix CPU initialization bug

ref #601
hw_arndale: create builddir support

ref #601
arndale: UART driver base

ref #601
arndale: board driver base

ref #601
cortex_a15: base/mk spec

ref #601
arndale: base/mk platform spec

ref #601
hw_arndale: enable nested init test

fix #601
base-hw: rework 'run/env', enable '--target uboot'

ref #601
ref #598
base-hw: provide SIGNAL service in nested_init.run

ref #601
base-hw: useless default assignment in syscalls.h

fix #588
base-hw: Adaptation to new base library layout

This is a follow-up fix of fae63f4fa9df237a5fa3d658b870def17e82f265

Fix #18