msm_rmnet_bam: Add support for IOCTL RMNET_IOCTL_DEREGISTER_DEV

msm_rmnet_bam registers platform drivers for multiple BAM_DMUX
channels on startup. The probe and remove events register and
unregister net devices respectively.

In scenarios where MAP protocol is used, these devices are treated
as physical devices and multiple virtual net devices are associated
with them. Multiple BAM_DMUX channels may not be used in such a case.
The unused channels add unnecessary delay during sub system restart.

Implement RMNET_IOCTL_DEREGISTER_DEV which will allow user space
modules to deregister a platform driver for a particular BAM_DMUX
channel.

CRs-Fixed: 738039
Change-Id: Id27bff8c59c36b00f4887492575dfb4e7c93198e
Acked-by: Nagarjuna Chaganti <nchagant@qti.qualcomm.com>
Signed-off-by: Ravinder Konka <rkonka@codeaurora.org>
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>