mtd: nand: omap: ecc.hwctl: rename omap3_enable_hwecc_bch to omap_enable_hwecc_bch

This patch
 - renames omap3_enable_hwecc_bch -> omap_enable_hwecc_bch to keep
   nomenclature independent of any device family.
 - using '__maybe_unused' instead of `ifdef based conditional compilation
   to suppress warning for un-used functions

Signed-off-by: Pekon Gupta <pekon@ti.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>