mmu: remove reinterpret_cast from get_mem_area_base()

Constant expression cannot have reinterpret_cast in any of its
subexpressions. As a result GCC 4.9 decides to call get_mem_area_base()
and initialize phys_mem at runtime. This is done when .init functions
are invoked, much later that the first use of phys_mem.

Signed-off-by: Paweł Dziepak <pdziepak@quarnos.org>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
mmu: use static_casts in translate_mem_area()

Signed-off-by: Paweł Dziepak <pdziepak@quarnos.org>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
mmu: make get_mem_area() static inline instead of constexpr

Because of use of reinterpret_cast that function cannot be a constant
expression anyway.

Signed-off-by: Paweł Dziepak <pdziepak@quarnos.org>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>