x86/vdso: Give the [ph]vclock_page declarations real types

Clean up the vDSO code a bit by giving pvclock_page and hvclock_page
their actual types instead of u8[PAGE_SIZE].  This shouldn't
materially affect the generated code.

Heavily based on a patch from Linus.

[ tglx: Adapted to the unified VDSO code ]

Co-developed-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/6920c5188f8658001af1fc56fd35b815706d300c.1561241273.git.luto@kernel.org