irq/platform-MSI: Increase the maximum MSIs the MSI framework can support

The current MSI framework can only support 256 platform MSIs. But on Hisilicon
platform, some network related devices has about 500 wired interrupts.

To support these devices and align with MSI-X increase the maximum to 2048
devices.

Signed-off-by: Ma Jun <majun258@huawei.com>
Cc: <Catalin.Marinas@arm.com>
Cc: <linux-arm-kernel@lists.infradead.org>
Cc: <Will.Deacon@arm.com>
Cc: <mark.rutland@arm.com>
Cc: <marc.zyngier@arm.com>
Cc: <jason@lakedaemon.net>
Cc: <lizefan@huawei.com>
Cc: <huxinwei@huawei.com>
Cc: <dingtianhong@huawei.com>
Cc: <liguozhu@hisilicon.com>
Cc: <guohanjun@huawei.com>
Link: http://lkml.kernel.org/r/1450752442-9392-1-git-send-email-majun258@huawei.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>