POST: Move QEMU specific ramsize and BIOS table setup to paravirt.c.

Don't clutter post.c with the gory details of QEMU memory sizing and
BIOS table creation.  Instead, move that code to paravirt.c.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
POST: Reorganize post entry and "preinit" functions.

Unlocking ram in handle_post() is tricky and only needed under qemu.
Separate out that logic from the coreboot/xen paths by invoking
handle_elf_post separately.  This simplifies both the qemu and
non-qemu code paths.

Also, organize all the "pre-init" functions into one section of the
file.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
POST: Move cpu caching and dma setup to platform_hardware_setup().

The CPU cache is enabled and DMA is disabled on all real-world POST
entry situations, so no need to do this in the low-level "pre-init"
phase.  Instead, move it to the platform hardware setup stage.

Also, move the setting of the reboot flags (which control reset-vector
entry point handling) to ivt_init().

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>