net: wan: fsl_qmc_hdlc: Convert carrier_lock spinlock to a mutex

In the Linux kernel, the following vulnerability has been resolved:

net: wan: fsl_qmc_hdlc: Convert carrier_lock spinlock to a mutex

The carrier_lock spinlock protects the carrier detection. While it is
held, framer_get_status() is called which in turn takes a mutex.
This is not correct and can lead to a deadlock.

A run with PROVE_LOCKING enabled detected the issue:
[ BUG: Invalid wait context ]
...
c204ddbc (&framer->mutex){+.+.}-{3:3}, at: framer_get_status+0x40/0x78
other info that might help us debug this:
context-{4:4}
2 locks held by ifconfig/146:
#0: c0926a38 (rtnl_mutex){+.+.}-{3:3}, at: devinet_ioctl+0x12c/0x664
#1: c2006a40 (&qmc_hdlc->carrier_lock){....}-{2:2}, at: qmc_hdlc_framer_set_carrier+0x30/0x98

Avoid the spinlock usage and convert carrier_lock to a mutex.