cpu: Add new get_phys_page_attrs_debug() method

cpu: Add new get_phys_page_attrs_debug() method

Add a new optional method get_phys_page_attrs_debug() to CPUClass.
This is like the existing get_phys_page_debug(), but also returns
the memory transaction attributes to use for the access.
This will be necessary for CPUs which have multiple address
spaces and use the attributes to select the correct address
space.

We provide a wrapper function cpu_get_phys_page_attrs_debug()
which falls back to the existing get_phys_page_debug(), so we
don't need to change every target CPU.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>