Add syscall for os_factory_hash()

[yrichard-ledger]

Description

Add new syscall for os_factory_hash() to read 32 bytes of data unique to the device.
This provides more entropy than os_serial()

Changes include

• Bugfix (non-breaking change that solves an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)
• Tests
• Documentation
• Other (for changes that might not fit in any category)

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (80b72e7) 69.33% compared to head (f134315) 69.33%.
Report is 7 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #393   +/-   ##
=======================================
  Coverage   69.33%   69.33%           
=======================================
  Files          11       11           
  Lines         874      874           
=======================================
  Hits          606      606           
  Misses        268      268           

Flag	Coverage Δ
unittests	69.33% <ø> (ø)

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