Instead of putting extra logic inside cpu.h, just do everything inside
cpu_x86_init_user().
Backports commit 15258d46baef5f8265ad5f1002905664cf58f051 from qem
Right now, the AVX512 registers are split in many different fields:
xmm_regs for the low 128 bits of the first 16 registers, ymmh_regs
for the next 128 bits of the same first 16 registers, zmmh_regs
for the next 256 bits of the same first 16 registers, and finally
hi16_zmm_regs for the full 512 bits of the second 16 bit registers.
This makes it simple to move data in and out of the xsave region,
but would be a nightmare for a hypothetical TCG implementation and
leads to a proliferation of [XYZ]MM_[BWLSQD] macros. Instead,
this patch marshals data manually from the xsave region to a single
32x512-bit array, simplifying the macro jungle and clarifying which
bits are in which vmstate subsection.
The migration format is unaffected.
Backports commit b7711471f551aa4419f9d46a11121f48ced422da from qemu
