ARM: 8589/1: asm/memory.h: remove dead definitions

The last ad-hoc __phys_to_virt definition was removed in commit fd0053c9


("ARM: realview: remove sparsemem hack"). Therefore we can remove the
unneeded definitions and unduplicate the virt_to_pfn macro from
asm/memory.h.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>