[RFC PATCH v6 0/2] Add file-backed and write-once features to OTP

[Green Wan]

Changelogs:
v5 to v6:
 - Rebase to latest. (sifive_u_otp.* are moved to hw/misc)
 - Put the example command to commit message.
 - Refine errp handle when check backend drive.
 - Remove unnecessary debug message.

v4 to v5:
 - Change the patch order
 - Add write operation to update pdin to fuse[] bit by bit 
 - Fix wrong protection for offset 0x0~0x38
 - Add SIFIVE_U_OTP_PWE_EN definition
 - Refine access macro for fuse[] and fuse_wo[]

Summary of Patches 
 - First patch is to add write opertion to update pdin data to fuse[] bit
   by bit. Add 'write-once' feature to block second write to same bit of
   the OTP memory.

 - Second patch is to add file-backed implementation to allow users to use
   '-drive' to assign an OTP raw image file. OTP image file must be bigger
   than 16K.

       For example, '-drive if=none,format=raw,file=otp.img'

Testing
 - Tested on sifive_u for both qemu and u-boot.

Green Wan (2):
  hw/misc/sifive_u_otp: Add write function and write-once protection
  hw/misc/sifive_u_otp: Add backend drive support

 hw/misc/sifive_u_otp.c         | 81 +++++++++++++++++++++++++++++++++-
 include/hw/misc/sifive_u_otp.h |  5 +++
 2 files changed, 85 insertions(+), 1 deletion(-)

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2.17.1