inmates: Add memory services to inmates framework

inmates: Add memory services to inmates framework

This adds a primitive memory allocator (without release) and a page
mapper (without unmap) to the inmates library. MMIO accessors are also
included. Those used for intercepted resources are encoded in assembly
to ensure that only supported instructions are used. With these
services, inmates can now access memory-mapped devices.

The allocator uses the lower memory starting from the first page.
Document this as well as the remaining memory layout.

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