ARM: dts: keystone: remove bogus IO resource entry from PCI binding

The PCI DT bindings contain a bogus entry for IO space which is not
supported on Keystone. The current bogus entry has an invalid size
and throws following error during boot.

[0.420713] keystone-pcie 21021000.pcie: error -22: failed to map
           resource [io  0x0000-0x400000003fff]

So remove it from the dts. While at it also add a bus-range
value that eliminates following log at boot up.

[0.420659] No bus range found for /soc/pcie@21020000, using [bus 00-ff]

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>