genirq/msi: Add MSI allocation helper and export MSI functions

MSI functions for allocation and free can be directly used by
the device drivers without any wrapper provided by bus drivers.
So export these MSI functions.

Also, add a wrapper API to allocate MSIs providing only the
number of interrupts rather than range for simpler driver usage.

Signed-off-by: Nipun Gupta <nipun.gupta@amd.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240423111021.1686144-1-nipun.gupta@amd.com


Signed-off-by: Alex Williamson <alex.williamson@redhat.com>