arch/x86: KABI structs and array padding

Bugzilla: https://bugzilla.redhat.com/2033081
Depends: https://bugzilla.redhat.com/2024595

Upstream Status: RHEL9 only

Add some initial KABI structs and padding to allow for expansion during
RHEL9.

• The apic and cpuinfo_x86 structs are directly exposed via the KABI
  whitelists. They are expanded by using RH_KABI_AUX_EMBED.
• Expand the x86 capability and bug registers to 30.
• The fpu and vdso_struct are internal-only structs and can be excluded
  from KABI.

To make this commit easier to find in future string searches:
RH_KABI kabi rh_kabi.

Signed-off-by: Prarit Bhargava prarit@redhat.com