PCI hotplug: ibmphp: read the length of ebda and map entire ebda region

ibmphp driver currently maps only 1KB of ebda memory area into kernel address
space during driver initialization. This causes kernel oops when the driver is
modprobe'd and it accesses memory beyond 1KB within ebda segment. The first
byte of ebda segment actually stores the length of the ebda region in
Kilobytes. Hence make use of the length parameter and map the entire ebda
region.

Signed-off-by: Chandru Siddalingappa <chandru@linux.vnet.ibm.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>