x86: qemu: Move Cache-As-RAM memory from area mapped to ROM

x86: qemu: Move Cache-As-RAM memory from area mapped to ROM

ROM has been made read-only in qemu recently (namely commit 208fa0e4:
"pc: make 'pc.rom' readonly when machine has PCI enabled"). So this
patch restores compatibility between U-Boot and qemu.

Signed-off-by: Anton Gerasimov <anton@advancedtelematic.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
[bmeng: mention qemu commit title in the commit message]
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>