updating encoding.h, added test for mconfigptr

[dansmathers]

Description

Add read-only CSR MCONFIGPTR test (1 read/1 write).

Related Issues

Requires sail update for signatures to pass: riscv/sail-riscv#293

Ratified/Unratified Extensions

• Ratified
• Unratified

List Extensions

MCONFIGPTR exists in the priv spec 1.12 and used by the discovery task group.

Reference Model Used

• SAIL
• Spike
• Other - < SPECIFY HERE >

Mandatory Checklist:

• [ X] All tests are compliant with the test-format spec present in this repo ?
• [ X] Ran the new tests on RISCOF with SAIL/Spike as reference model successfully ?
  requires Add read-only CSR MCONFIGPTR riscv/sail-riscv#293 and reference this issue to workaround SAIL compile issue: sail compile temp broken. riscv/sail-riscv#292
• Ran the new tests on RISCOF in coverage mode
• Link to Google-Drive folder containing the new coverage reports (See this for more info): < SPECIFY HERE >
• Link to PR in RISCV-ISAC from which the reports were generated : < SPECIFY HERE >
• Changelog entry created with a minor patch

Optional Checklist:

• RISCV-V CTG PR link if tests were generated using it : < SPECIFY HERE >
• Were the tests hand-written/modified ?
• Have you run these on any hard DUT model ? Please specify name and provide link if possible in the description
• If you have modified arch_test.h Please provide a detailed description of the changes in the Description section above.

[dansmathers]

closing. Not sure how to have more than one fork at a time. since these are technical debt, no rush. will open a new pull for smcsrind.