hwrng: omap - Set default quality

Newer combinations of the glibc, kernel and openssh can result in long initial
startup times on OMAP devices:

[    6.671425] systemd-rc-once[102]: Creating ED25519 key; this may take some time ...
[  142.652491] systemd-rc-once[102]: Creating ED25519 key; done.

due to the blocking getrandom(2) system call:

[  142.610335] random: crng init done

Set the quality level for the omap hwrng driver allowing the kernel to use the
hwrng as an entropy source at boot.

Signed-off-by: Rouven Czerwinski <r.czerwinski@pengutronix.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>