Because of the way the Linux code behind apldrm(4) is structured it may

Because of the way the Linux code behind apldrm(4) is structured it may
fail to create a framebuffer without propagating an error to its callers.
Prevent a kernel panic by explicitly checking that we have a framebuffer.
To prevent us ending up with no framebuffer at all, only claim the
framebuffer in apldrm(4) when we actually created our own.  Delay the
attach of simplefb(4) such that we check whether someone else claimed its
framebuffer until apldrm(4) has done its thing.

tested by robert@
ok jsg@