Add Design Documentation of MMU SV32

Created by: YazanHussnain-10x

This Pull Request adds the design documentation for MMU SV32 and resolve this issue openhwgroup/cva6#1393, covering several critical modules. The following modules are documented within this pull request:

1. MMU SV32: This section provides an in-depth overview of the MMU SV32 module.

2. Translation Lookaside Buffer (TLB): This part of the documentation delves into the details of the TLB module.

3. Shared TLB: The documentation further extends to cover the Shared TLB module, explaining how it works and its features.

4. Page Table Walker (PTW): The PTW module is thoroughly explored in this documentation, shedding light on its functionality and design.

Within each of these modules, various sections are covered, ensuring a comprehensive understanding of their operation. Here's a breakdown of the sections for each module:

MMU SV32:

• Introduction
• Signal Description of MMU SV32
• Struct Description
• Control Flow
• Instruction Fetch Interface
• Data Interface

TLB:

• Introduction
• Signal Description of TLB
• Struct Description
• TLB Entry Fields
• TLB Implementation in CVA6
• TLB Lookup
• Update and Flush
• Replacement Policy

Shared TLB:

• *Introduction
• Signal Description of Shared TLB
• Struct Description
• Shared TLB Entry Fields
• Shared TLB Implementation in CVA6
• Shared TLB Lookup
• Update and Flush
• Replacement Policies

PTW:

• Introduction
• Signal Description of PTW
• Struct Description
• PTW State Machine
• All States
• Flush Scenario