x86/cpu: Use XGETBV and XSETBV mnemonics in fpu/internal.h

Current minimum required version of binutils is 2.23, which supports
XGETBV and XSETBV instruction mnemonics.

Replace the byte-wise specification of XGETBV and XSETBV with these
proper mnemonics.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200707174722.58651-1-ubizjak@gmail.com