MFC part of r267973: remove redundant "" assignment for string in BSS.

Sponsored by:	The FreeBSD Foundation
MFC r268771, r268796 by nwhitehorn:

r268771:
  Allow console drivers active from early boot to be used with
  xf86-video-scfb, rather than only drivers attached later on. This
  involves a small amount of code duplication with dev/fb/fbd.c, which
  will fixed later on.

  Also improve performance of vt_blank() by making it not read from the
  framebuffer unnecessarily.

r268796:
  Fix embarassing typos I made.

Sponsored by:	The FreeBSD Foundation
MFC r268772 by nwhitehorn:

  Allow efifb to be used with xf86-video-scfb. This is important for EFI
  systems without either a CSM or real graphics drivers, such as my
  Lenovo Haswell laptop.

  This provides working X with the small complication of a console
  cursor permanently overlaid on the upper-left corner of the screen
  that will be dealt with later.

  Also remove some redundant screen clearing.

Sponsored by:	The FreeBSD Foundation