core: rename per_cpu variable flush_virt_caches to flush_vcpu_caches

Also changed the comment to hopefully better reflect what the variable
is used for.

Signed-off-by: Henning Schild <henning.schild@siemens.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
control: add a control function to flush vcpu caches of a whole cell

When having to unmap memory while a cell is running we need a way to
flush its tlbs. Adding a function to do just that.

Signed-off-by: Henning Schild <henning.schild@siemens.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
x86: control: use arch_flush_cell_vcpu_caches in arch_config_commit

Use the new function also in arch_config_commit to get that function
more compact.

Signed-off-by: Henning Schild <henning.schild@siemens.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>