Fixup integer types

[SamTebbs33]

There are some cases where a u32 is used but a usize is better as it would scale up on a 64 bit architecture. These should be changed to make the code more versatile.

Found culprits are:

• kmap_end and kmap_start in panic.init should be declared as usize
• mod_start and mod_end in panic.init should be casted to a usize
• arch.MEMORY_BLOCK_SIZE, pmm.BLOCK_SIZE and vmm.BLOCK_SIZE should be usize
• mem.MemProfile.mem_kb
• Bitmap.init should accept the number of entries as a usize
• Bitmap types should use usize as the entry type