hw/ide/isa: Extract TYPE_ISA_IDE declarations to 'hw/ide/isa.h'

hw/ide/isa: Extract TYPE_ISA_IDE declarations to 'hw/ide/isa.h'

"hw/ide.h" is a mixed bag of lost IDE declarations.

Extract isa_ide_init() and the TYPE_ISA_IDE QOM declarations
to a new "hw/ide/isa.h" header.

Rename ISAIDEState::isairq as 'irqnum' to emphasize this is
not a qemu_irq object but the number (index) of an ISA IRQ.

Message-Id: <20230215112712.23110-5-philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Bernhard Beschow <shentey@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>