iommu: Align QCOM_IOMMU_IO_PGTABLE_QUIRKS with other configs

The IOMMU configs should not be enabled unless we are sure
that we need to use them, so align the description for
QCOM_IOMMU_IO_PGTABLE_QUIRKS to reflect this.

Change-Id: I62893ae6f263200417f69ffdd559f9601241f9f2
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>