Use _vectab instead of Lvectab, which is moving to .data

Use _vectab instead of Lvectab, which is moving to .data

From NetBSD:
Add floppy index interrupt processing.

Startup modified to work with kernel loaded directly into fast memory.
This removes the need to have enough chip memory to load the kernel
when booting.  Kernel memory is dual-mapped (VA == 0 and VA == PA)
for enabling the MMU, and the VA == PA mapping removed after start_c()
has completed.  Chip memory is still required for the /dev/reload
process.