ARM: OMAP2+: Mark omap_hsmmc_init and omap_mux related functions as __init

Now that omap hsmmc init is split into two functions, it's safe
to mark omap_hsmmc_init and omap_mux related functions to __init.

This basically reverts the following fixes for the case where
TWL was compiled as a module:

a98f77bb (ARM: omap: fix section mismatch warning for sdp3430_twl_gpio_setup())
8930b4e3 (ARM: omap: fix section mismatch warnings in mux.c caused by hsmmc.c)

Additionally it fixes up the remaining section warnings for
all callers of omap_mux functions.

Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Tony Lindgren <tony@atomide.com>