Implement ioremap_prot() to allow mapping IO memory with variable
protection
via TLB.

Implementing this allows the /dev/mem driver to use its generic access()
VMA callback, which in turn allows ptrace to examine data in memory
mapped regions mapped via /dev/mem, such as Arc DCCM.

The end result is that it is possible to examine values of variables
placed into DCCM in user space programs via GDB.

CC: Alexey Brodkin <Alexey.Brodkin@synopsys.com>
CC: Noam Camus <noamc@ezchip.com>
Acked-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>