x86/hyperv: Implement hypervisor RAM collection into vmcore

x86/hyperv: Implement hypervisor RAM collection into vmcore

Introduce a new file to implement collection of hypervisor RAM into the
vmcore collected by linux. By default, the hypervisor RAM is locked, ie,
protected via hw page table. Hyper-V implements a disable hypercall which
essentially devirtualizes the system on the fly. This mechanism makes the
hypervisor RAM accessible to linux. Because the hypervisor RAM is already
mapped into linux address space (as reserved RAM), it is automatically
collected into the vmcore without extra work. More details of the
implementation are available in the file prologue.

Signed-off-by: Mukesh Rathor <mrathor@linux.microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>