bcm2835_mbox/property: replace ldl_phys/stl_phys with endian-specific accesses

bcm2835_mbox/property: replace ldl_phys/stl_phys with endian-specific accesses

PMM pointed out that ldl_phys and stl_phys are dependent on the CPU's
endianness, whereas device model code should be independent of
it. This changes the relevant Raspberry Pi devices to explicitly call
the little-endian variants.

Signed-off-by: Andrew Baumann <Andrew.Baumann@microsoft.com>
Message-id: 1456880233-22568-1-git-send-email-Andrew.Baumann@microsoft.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>