inmates: Map Comm Region always at 0x100000 for inmates framework

inmates: Map Comm Region always at 0x100000 for inmates framework

Standardize mapping and access to the Comm Region within the inmates
framework. Reduces the work to be done for new inmates. We will move it
higher once paging services are available so that larger inmates can be
created.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>