remoteproc: Introduce deny_sysfs_ops flag

The remoteproc framework provides sysfs interfaces for changing
the firmware name and for starting/stopping a remote processor
through the sysfs files 'state' and 'firmware'. These interfaces
are currently allowed irrespective of how the remoteprocs were
booted (like remoteproc self auto-boot, remoteproc client-driven
boot etc). These interfaces can adversely affect a remoteproc
and its clients especially when a remoteproc is being controlled
by a remoteproc client driver(s). Also, not all remoteproc
drivers may want to support the sysfs interfaces by default.

Add support to deny the sysfs state/firmware change by introducing
a state flag 'deny_sysfs_ops' that the individual remoteproc drivers
can set based on their usage needs. The default behavior is to
allow the sysfs operations as before.

Signed-off-by: Suman Anna <s-anna@ti.com>