[riscv] Clean up code structure and style in all RISC-V files and code sections

[waddlesplash]

During the RISC-V port bringup, a lot of code is being imported with structures and styles (especially variable naming, linebreak placement, usages of constants, especially machine constants in the bootloader) that is very much out of convention with Haiku standards and practices.

Examples:

• Function and variable naming (e.g. SignExtendVirtAdr, etc.)
• Global constants (e.g. (1 << pteRead) is used everywhere instead of pteRead being defined appropriately)
• Debugging code (e.g. in the EFI loader, potentially removable altogether)
• Additions of ___riscv ifdefs in the bootloader, kernel, and elsewhere in general code where it should not be needed, and instead removed.