x86/fpu/xstate: Separate user and supervisor xfeatures mask

Before the introduction of XSAVES supervisor states, 'xfeatures_mask' is
used at various places to determine XSAVE buffer components and XCR0 bits.
It contains only user xstates.  To support supervisor xstates, it is
necessary to separate user and supervisor xstates:

- First, change 'xfeatures_mask' to 'xfeatures_mask_all', which represents
  the full set of bits that should ever be set in a kernel XSAVE buffer.
- Introduce xfeatures_mask_supervisor() and xfeatures_mask_user() to
  extract relevant xfeatures from xfeatures_mask_all.

Co-developed-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://lkml.kernel.org/r/20200512145444.15483-4-yu-cheng.yu@intel.com