iommu/omap: Enable bus-error back on supported iommus

The remoteproc MMUs in OMAP4+ SoCs have some additional debug
registers that can give out the PC value in addition to the
MMU fault address. The PC value can be extracted properly only
on the DSP cores, and is not available on the ARM processors
within the IPU sub-systems. Instead, the MMUs have been enhanced
to throw a bus-error response back to the IPU processors.

This functionality is programmable through the MMU_GP_REG register.
The cores are simply stalled if the MMU_GP_REG.BUS_ERR_BACK_EN bit
is not set. When set, a bus-error exception is raised allowing the
processor to handle it as a bus fault and provide additional debug
information. This feature is turned on by default by the driver on
iommus supporting it.

Signed-off-by: Subramaniam Chanderashekarapuram <subramaniam.ca@ti.com>
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Joerg Roedel <joro@8bytes.org>