Merge the document for Stage 1: memory management and SBI
合并第一阶段设计文档：SBI调用规范与RustSBI可用接口、内存管理模块。开始操作系统功能实现。
Merge the following document for Stage 1:
- Memory management module and its interface
- SBI calling convention and RustSBI available interface
Initiate implementation task of the OS functional requirements in Stage 1:
-
SBI doc -
Trap handler doc -
Memory management doc -
Boot framework -
Trap handler module -
Memory management module