hw/mips: Inline 'bios.h' definitions

There is no universal BIOS, each machine needs a specific one.

Move the machine-specific definitions to each machine code and
remove this bogus header.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20231122184334.18201-1-philmd@linaro.org>