x86: 32-bit: restore virtual linking capability

This reverts commit 7d32e9f9.

We now allow the kernel to be linked virtually. This patch:

- Properly converts between virtual/physical addresses
- Handles early boot instruction pointer transition
- Double-maps SRAM to both virtual and physical locations
  in boot page tables to facilitate instruction pointer
  transition, with logic to clean this up after completed.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
Signed-off-by: Daniel Leung <daniel.leung@intel.com>