xl: implement parsing of cpuid parameter and translate to Xen interface

xl: implement parsing of cpuid parameter and translate to Xen interface

Parses a string enumerating cpuid flags and their behavior.
The syntax is: cpuid = "host,<flagname>=[01xks],..."
Supports:
0: clear this flag
1: set this flag
x: don't care, use the default handling
k: use the host value
s: as k, but keep stable across migrations

For multiple bit flags there have to be numbers passed (hex or dec),
like: family=0x10,model=4

Signed-off-by: Andre Przywara <andre.przywara@amd.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
committer: Stefano Stabellini <stefano.stabellini@eu.citrix.com>