x86/kaslr: Make local variables 64-bit

Change the type of local variables/fields that store mem_vector
addresses to u64 to make it less likely that 32-bit overflow will cause
issues on 32-bit.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200728225722.67457-21-nivedita@alum.mit.edu