- When we restore VESA state, try BIOS POST earlier. VESA restore state

- When we restore VESA state, try BIOS POST earlier.  VESA restore state
function may not work properly if we don't.  Turn off hardware cursor as
vesa_set_mode() does.
- Add VBE 3.0 specific fields in VESA mode structure and pack it.  Note
the padding is 190 bytes although VBE 3.0 says 189 bytes.  It must be wrong
because the size of structure becomes 255 bytes and the specification says
it must be 256 bytes in total.  In fact, an example code in the spec. does
it right, though.  While we are at it, fix some i386-isms.
- Remove state buffer size limitation.  It is no longer necessary since
sys/compat/x86bios/x86bios.c r198251.
- Move int 0x10 vector test into vesa_bios_post() as we always do it anyway.