[FAQ] SYSFW keyring importing support on AM62x

1/. Generate and sign the keyring import certificate
a. untar the package "keyring_gen_sign.tar.xz"
b. read "README.md" on how to generate and sign the keyring import certificate
c. sample cmds are listed below, which generate the keyring import certificate "keyring_init.h"
- "python3 gen_keyring.py"
- "python3 sign_keyring.py './keys/root/custMpk.pem' 6 0"

2/. u-boot patches (keyring-patch.tar.xz)
Apply the following u-boot patches
- 0001-tisci-driver-for-sysfw-keyring-import-API.patch: tisci driver for sysfw keyring import API
- 0001-calling-sysfw-keyring-import-API-in-r5-spl.patch: calling sysfw keyring import API in r5-spl
- 0001-tisci-cmd-to-verify-bin-via-TISCI-API: test cmd to verify the test binary signed with the imported key

3/. Sign test binary with the imported key
run "./sign_bin.sh" from the above untared folder in step #1 above
- sign the test binary with the imported key for positive test
- sign the test binary with the un-imported key for negative test

4/. Test log (am62_11.1.5.3_keyring.log)
- SYSFW/TIFS keyring import API is called in u-boot (r5-spl)
- u-boot test cmds to verify two test binary, where one (signed_1.bin) is signed with the imported key (positive test), and one (signed_7.bin) signed with the un-imported key (negative test)
- sample u-boot test cmd from SD boot, where signed_1.bin & signed_7.bin are copied to SD boot partition

load mmc 1 $loadaddr signed_1.bin; tisci_verify $loadaddr $filesize
load mmc 1 $loadaddr signed_7.bin; tisci_verify $loadaddr $filesize

https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/791/7120.keyring_5F00_gen_5F00_sign.tar.xz

https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/791/keyring_2D00_patch.tar.xz

am62_11.1.5.3_keyring.log