script/imgedit.py: Remove the usage of O_DIRECT by qemu-nbd.

This prevented the script to work on tmpfs.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
x64: Use constants for CR0 and CR4 values

Replace magic numbers with constants for CR0 and CR4 control register
values in arch/x86/boot.S.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>