xen/arm: platform: Add Raspberry Pi platform

xen/arm: platform: Add Raspberry Pi platform

The aux peripherals (uart1, spi1, and spi2) share an IRQ and a page of
memory. For debugging, it is helpful to use the aux UART in Xen. In
this case, Xen would try to assign spi1 and spi2 to dom0, but this
results in an error since the shared IRQ was already assigned to Xen.
Blacklist aux devices other than the UART to prevent mapping the shared
IRQ and memory range to dom0.

Blacklisting spi1 and spi2 unfortunately makes those peripherals
unavailable for use in the system. Future work could include forwarding
the IRQ for spi1 and spi2, and trap and mediate access to the memory
range for spi1 and spi2.

Signed-off-by: Stewart Hildebrand <stewart.hildebrand@dornerworks.com>
Acked-by: Julien Grall <julien.grall@arm.com>