Isolate sc 1 detection logic

Under weird circumstances we ended up with unsynchronized data and text
section references between the stage1 and paflof binaries.

This patch moves the initial sc 1 detection logic to work without any
persistent state, making it properly reentrant regardless of the place
we end up hitting the code at.

This fixes broken sc 1 detection for me on PR KVM.

Signed-off-by: Alexander Graf <agraf@suse.de>
[aik: added r0 to clobber list and $(FLAG) to AS1FLAGS as suggested by agraf, tested on pHyp]
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
version: update to 20140404

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>