hw: make Processor_client::_processor protected

ref #1126
hw: turn Cortex_a9::Processor_driver into a class

ref #1126
hw & rpi: provide Pic::MAX_INTERRUPT_ID

ref #1126
hw & cortex_a9: do lazy FPU-context switch

ref #1126
base & cortex_a9: enable FPU

ref #1126
base: test for the pseudo-parallel use of an FPU

fix #1126
backtrace.diff
backtrace_c.diff
issue1132.diff
issue1134.diff
issue1136.diff
issue1137.diff
ldso_show_link_addr.diff
qt5_arm.diff
blit_debug.diff
lx_emul_mb.diff