configs: qemu: add a virtual PCI device to qemu config

This adds a virtual PCI device of type ivshmem to the root-cell on qemu.
Starting a cell with an ivshmem at the same bdf, refering to the same
memory will allow the two cells to connect.

Signed-off-by: Henning Schild <henning.schild@siemens.com>
[Jan: adjusted memory regions to avoid overlappings]
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
docs: add documentation for inter-cell communication

Signed-off-by: Henning Schild <henning.schild@siemens.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
inmates: x86: Account for rounding of region address in map_range

When feeding in a start address that is not huge-page aligned, we will
let the mapping start earlier, thus also have to extend the size.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
docs: inter-cell: Add pointer to root-cell test code

Adding a section on how to play with inter-cell communication and where
to find the Linux test code.

Signed-off-by: Henning Schild <henning.schild@siemens.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
core: Fix asm-defines.h dependencies tracking

Previously, a change to headers like <asm/percpu.h> didn't trigger
a rebuild of asm-defines.s (thus asm-defines.h). This is fixed now.

Signed-off-by: Valentine Sinitsyn <valentine.sinitsyn@gmail.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>