hw/avr: Prepare for TARGET_PAGE_SIZE > 256

If i/o does not cover the entire first page, allocate a portion
of ram as an i/o device, so that the entire first page is i/o.

While memory_region_init_ram_device_ptr is happy to allocate
the RAMBlock, it does not register the ram for migration.
Do this by hand.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2 files changed