This patch replaces the existing OsLayer::VirtualToPhysical stub with

This patch replaces the existing OsLayer::VirtualToPhysical stub with
an actual implementation that translates addresses via the Linux
/proc/self/pagemap interface. This causes failing memory locations to
be reported with both virtual and physical address, and facilitates
isolating a defective memory module.

Like many other functions currently implemented in the generic OsLayer
class, this functionality is specific to Linux and would need to be
moved to a respective subclass if proper multi-OS support ever gets
implemented.

Signed-off-by: Julius Werner <jwerner@chromium.org>