hw/i386/pc: Rename bochs_bios_init as more generic fw_cfg_arch_create

The bochs_bios_init() function is not restricted to the Bochs
BIOS and is useful to other BIOS.
Since it is not specific to the PC machine, and can be reused
by other machines of the X86 architecture, rename it as
fw_cfg_arch_create().

Suggested-by: Samuel Ortiz <sameo@linux.intel.com>
Reviewed-by: Li Qiang <liq3ea@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20190818225414.22590-5-philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>