omap: add support for the TRNG Hardware Accelerator

omap: add support for the TRNG Hardware Accelerator

According to TI docs (Processor SDK Linux Getting Started Guide)
the Random Number Generator hardware is found on
OMAP16xx, OMAP2/3/4/5, AM33xx/AM43xx boards. It already
defined in device tree files. Let's enable it.

Some tests:

root@RTS1_OI:~# rngtest -c 1000 </dev/hwrng
rngtest 6.10
Copyright (c) 2004 by Henrique de Moraes Holschuh
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.

rngtest: starting FIPS tests...
rngtest: bits received from input: 20000032
rngtest: FIPS 140-2 successes: 999
rngtest: FIPS 140-2 failures: 1
rngtest: FIPS 140-2(2001-10-10) Monobit: 0
rngtest: FIPS 140-2(2001-10-10) Poker: 0
rngtest: FIPS 140-2(2001-10-10) Runs: 1
rngtest: FIPS 140-2(2001-10-10) Long run: 0
rngtest: FIPS 140-2(2001-10-10) Continuous run: 0
rngtest: input channel speed: (min=198.710; avg=1265.501; max=2976.417)Kibits/s
rngtest: FIPS tests speed: (min=1.780; avg=37.085; max=39.736)Mibits/s
rngtest: Program run time: 15961329 microseconds

Signed-off-by: Alexey Smirnov <s.alexey@gmail.com>