Drivers: hv: vmbus: include header for get_irq_regs()

[ Upstream commit b9fcc1867cc7921bb8441be327ed58461ed12255 ]

On !RT the header file get_irq_regs() gets pulled in via other header files. On
RT it does not and the build fails:

    drivers/hv/vmbus_drv.c:975 implicit declaration of function ‘get_irq_regs’ [-Werror=implicit-function-declaration]
    drivers/hv/hv.c:115 implicit declaration of function ‘get_irq_regs’ [-Werror=implicit-function-declaration]

Add the header file for get_irq_regs() in a common header so it used by
vmbus_drv.c by hv.c for their get_irq_regs() usage.

Reported-by: Bernhard Landauer <oberon@manjaro.org>
Reported-by: Ralf Ramsauer <ralf.ramsauer@oth-regensburg.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>