fbaccel: add hack on spark to avoid too frequent blitting

Conflicts:
	src/driver/fbaccel.cpp
fbaccel: use the same blit-limiting hack on spark and azbox

TODO: test on other architectures, simplify code

Conflicts:
	src/driver/fbaccel.cpp
azbox: default to manual blitting

to check if kernel-autoblit is getting usable, use
"AZBOX_KERNEL_BLIT=1" environment variable
fbaccel: auto-blit, obsoleting the explicit blit() calls

probably needs refining on some platforms

Conflicts:
	src/driver/fbaccel.cpp
	src/driver/framebuffer_ng.cpp
	src/driver/framebuffer_ng.h
fbaccel: always blit every 250ms

this fixes problems with plugins that write directly into the
framebuffer (tuxtxt for example)

Conflicts:
	src/driver/fbaccel.cpp
fbaccel: don't blit in waitForIdle() on spark

seems like it is not really needed, avoids too frequent blits
fbaccel: factor out private stuff into own header

Conflicts:
	src/driver/fbaccel.cpp
	src/driver/framebuffer_ng.h
framebuffer-ng: move hw-specific stuff into fbaccel

hardware initialization is platform specific, so put
it into fbaccel instead.

Conflicts:
	src/driver/fbaccel.cpp
framebuffer-ng: move more hw specific stuff to fbaccel

setMode (not really the right name) is also hardware specific,
so move it into fbaccel, too.

Conflicts:
	src/driver/framebuffer_ng.cpp
fbaccel: get rid of USE_OPENGL

it's not really OpenGL we are using but glfb, and this is on
all generic-hw boxes, so use the HAVE_GENERIC_HARDWARE define.