tools: arm: prepare guest FDT building for multiple RAM banks

tools: arm: prepare guest FDT building for multiple RAM banks

This required exposing the sizes of the banks determined by the domain builder
up to libxl via xc_dom_image.

Since the domain build needs to know the size of the DTB we create placeholder
nodes for each possible bank and when we finalise the DTB we fill in the ones
which are actually populated and NOP out the rest.

Note that the number of guest RAM banks is still 1 after this change.

Also fixes a coding style violation in
libxl__arch_domain_finalise_hw_description while there.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Julien Grall <julien.grall@linaro.org>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
[ ijc -- minor coding style fix ]