remoteproc: pru: Fix loading of GNU Binutils ELF

PRU port of GNU Binutils lacks support for separate address spaces.
PRU IRAM addresses are marked with artificial offset to differentiate
them from DRAM addresses. Hence remoteproc must mask IRAM addresses
coming from GNU ELF in order to get the true hardware address.

PRU firmware used for testing was the example in:
  https://github.com/dinuxbg/pru-gcc-examples/tree/master/blinking-led/pru



Signed-off-by: Dimitar Dimitrov <dimitar@dinux.eu>
Link: https://lore.kernel.org/r/20201230105005.30492-1-dimitar@dinux.eu


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>