gpu: host1x: Correct allocated size for contexts

gpu: host1x: Correct allocated size for contexts

[ Upstream commit e889a311f74f4ae8bd40755a2c58d02e1c684fef ]

Original implementation over allocates the memory size for the
contexts list. The size of memory for the contexts list is based
on the number of iommu groups specified in the device tree.

Fixes: 8aa5bcb61612 ("gpu: host1x: Add context device management code")
Signed-off-by: Johnny Liu <johnliu@nvidia.com>
Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230901115910.701518-1-cyndis@kapsi.fi
Signed-off-by: Sasha Levin <sashal@kernel.org>