Explicitly include that header to avoid build errors when vzalloc()
becomes "invisible" to the compiler due to header reorganizations.

This is not a problem in the tip tree but occurred when integrating
linux-next.

 [ bp: Commit message. ]

Link: https://lore.kernel.org/r/20211025151144.552c60ca@canb.auug.org.au
Fixes: 69f6ed1d ("x86/fpu: Provide infrastructure for KVM FPU cleanup")
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Borislav Petkov <bp@suse.de>