The uart_handle_cts_change() and uart_handle_dcd_change() must be called
with port lock being held. Acquire the lock after reading MSR register.
Do not acquire spin lock when reading MSR register because I2C/SPI port
functions cannot be called with spinlocks held.

Update rng and dsr counters. Wake up delta_msr_wait to allow tty notice
modem status change.
Co-developed-by: NLech Perczak <l.perczak@camlintechnologies.com>
Co-developed-by: NTomasz Moń <tomasz.mon@camlingroup.com>
Signed-off-by: NLech Perczak <l.perczak@camlintechnologies.com>
Signed-off-by: NTomasz Moń <tomasz.mon@camlingroup.com>
Link: https://lore.kernel.org/r/20220301060332.2561851-3-tomasz.mon@camlingroup.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>