usr: Create objectfile for usr filesystem using .incbin

usr: Create objectfile for usr filesystem using .incbin

Patch originally by HJ Lu.

The filesystem was previously embedded in a .o file using ld.
Embedding the filesystem using ld broke as a result ia64 and maybe more
architectures.

The better way to do this is to use the .incbin feature, as already
used for vsyscall for i386. .incbin has the advantage that ELH header
is correct, as required by ia64 - and maybe other archs.
This change will break architectures relying on binutils older than
2.11.90.0.23 released on 2001-07-14.
Most notably arm will break in some configurations due to this.
The rationale behing introducing .incbin is that ia64 needs this change
and the .incbin feature has been present in binutils for a number
of years now.
arm will thus have to catch up with binutils - or patch usr/Makefile
to stay compatible with the 2.5 kernel.

The definition of LDFLAGS_BLOB removed for all architectures - it was
obsoleted by this change.
Except for arm - that may require it due to the tool compatibility issue.