OMAP2+: hwmod: Remove omap_hwmod_mutex

The hwmod list will be built are init time and never
be modified at runtime. There is no need anymore to protect
the list from concurrent accesses using a mutex.

Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>