[EGD-4863] Add harness test for cellular sleep mode

Adding test for outgoing call and text message
in cellular sleep mode

[EGD-4852] Add sleep mode for GSM modem

When the GSM modem is idle and there is no communication,
it enters the sleep mode, where the power consumption
is significantly reduced.

[EGD-5868] Add access to backup over MTP

This change adds access to backups via MTP
after backup file has been successfuly created.

[EGD-6111] Timers refactored

Deep refactor of system timers.

[EGD-5814] Fix battery revert

Revert of temporary fix
for old battery operation

[EGD-6237] Add memory clearing of MTP database storage

Clear allocated memory to avoid occasional HFs due to accessing
trashed entries

[EGD-6192] Add torch hw control v2

Change behavior of torch
control according to newest
design.

[EGD-4851] Add URC support in sleep mode

When URCs come from the network and GSM is in sleep mode,
we wake up the modem to properly handle the incoming data.

[EGD-5229] Cellular modem, change receiving to DMA

Changes implementation for receiving data from
cellular modem from IRQ byte-by-byte to DMA transactions.
Drop in replacement, works with current CMUX (TS07.10)

[EGD-5101] Add flow control configuration for cellular

Fix flow control pin configuration in OS.
Turn on flow control for cellular modem.

[EGD-6067] Fix database performance issues

New filesystem works differently and some vFAT optimizations
backfired badly after switch.

- avoid unnecessary folder traversing
- eliminate some unnecessary fstats
- rework sqlite file driver
- reduce MMC startup delay
- fix errno bug in iosyscalls

[EGD-6100] Add BT device turn off handling

After BT device disconnects (e.g. because of shutdown) Pure is now
aware of this

[EGD-5512] Usb security refactor and devices pairing

Move all security related functionality to single security endpoint
Paired devices can be added to avoid further passcode requests

[EGD-4853] Add Wake up GSM modem on demand

System wakes up Cellular when there is a need to communicate
with the modem, e.g. to handle an outgoing call

[EGD-5660] Add PWM Cpu sentinel

Change of PWM frequency due
to main clock change in low
power operation.

[EGD-5204] Secure USB communication

Secure all endpoints by returning 403(Forbidden) when USB is connected.
Request screen passcode to enable secured endpoints.

Merge branch 'EGD-5737-merge-master-to-exp-lbr-fix'

[EGD-5565] USB: Fix stack size for littlefs

Update USB submodule

[EGD-5737] Fix compilation issues after merge

Master was using some fetures removed by new filesystem

[EGD-5737] Merge master into experimental

Synchronize with master before merging