x86/svm: Drop enum instruction_index and simplify svm_get_insn_len()

x86/svm: Drop enum instruction_index and simplify svm_get_insn_len()

Passing a 32-bit integer index into an array with entries containing less than
32 bits of data is wasteful, and creates an unnecessary error condition of
passing an out-of-range index.

The width of the X86EMUL_OPC() encoding is currently 20 bits for the
instructions used, which leaves room for a modrm byte.  Drop opc_tab[]
entirely, and encode the expected opcode/modrm information directly.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Brian Woods <brian.woods@amd.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Juergen Gross <jgross@suse.com>