ACPICA: Do not touch VGA memory when EBDA < 1ki_b

ACPICA: Do not touch VGA memory when EBDA < 1ki_b

ACPICA commit a36eda9631e84f271319c41288889dd5b1329369

The ACPICA code assumes that EBDA region must be at least 1ki_b in size.
Because this is not guaranteed, it might happen that while scanning the
memory for RSDP pointer, the kernel touches memory above 640ki_b.

This is unwanted as the VGA memory range may not be decoded or
even present when running under virtualization.

Link: https://github.com/acpica/acpica/commit/a36eda96
Signed-off-by: Vit Kabele <vit@kabele.me>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>