fbcon: remove broken mac vbl handler

Remove the Mac VBL interrupt code as it doesn't work properly and
doesn't bring any benefit when fixed. Also remove unused
DEFAULT_CURSOR_BLINK_RATE macro and irqres variable.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>