remoteproc: Add a sysfs interface for name

This patch adds a sysfs interface that provides the name of the
remote processor to userspace. This allows the userspace to identify
a remote processor as the remoteproc devices themselves are created
based on probe order and can change from one boot to another or
at runtime.

The name is made available in debugfs originally, and is being
retained for now. This can be cleaned up after couple of releases
once users get familiar with the new interface.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>