Replace cpu_physical_memory_rw were possible

Replace cpu_physical_memory_rw were possible

Using cpu_physical_memory_read, cpu_physical_memory_write and ldub_phys
improves readability and allows removing some type casts.

lduw_phys and ldl_phys were not used because both require aligned
addresses. Therefore it is not possible to simply replace existing
calls by one of these functions.

Signed-off-by: Stefan Weil <[email protected]>
Signed-off-by: Aurelien Jarno <[email protected]>