x86/sev: Return an error on a returned non-zero SW_EXITINFO1[31:0]

After returning from a VMGEXIT NAE event, SW_EXITINFO1[31:0] is checked
for a value of 1, which indicates an error and that SW_EXITINFO2
contains exception information. However, future versions of the GHCB
specification may define new values for SW_EXITINFO1[31:0], so really
any non-zero value should be treated as an error.

Fixes: 597cfe48

 ("x86/boot/compressed/64: Setup a GHCB-based VC Exception handler")
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: <stable@vger.kernel.org> # 5.10+
Link: https://lkml.kernel.org/r/efc772af831e9e7f517f0439b13b41f56bad8784.1633063321.git.thomas.lendacky@amd.com