hh_dbl: fix a race condition while vm is booting

When VM is booting, neuron driver can send a request to PVM using doorbell.
Currently this call is racing with when the doorbell driver is getting
the resources from the RM driver. Prevent clients to send a message when
resources are not ready. Added locking in function to check whether
resources are ready are not.

Unable to handle kernel NULL pointer dereference at virtual address 0x0
__wake_up_common+0x88/0x190
__wake_up+0x78/0xc0
hh_dbl_populate_cap_info+0xf4/0x1f8
hh_rm_populate_hyp_res+0x17c/0x2d0
hh_rm_get_svm_res_work_fn+0x34/0x78
process_one_work+0x214/0x468
worker_thread+0x330/0x4c0
kthread+0x134/0x148.

Change-Id: Id66b2d6382f33260dbb4c8d069c9fe5bc41e52fe
Signed-off-by: Murali Nalajala <mnalajal@codeaurora.org>