ARM: OMAP2+: gpmc: update gpmc_hwecc_bch_capable() for new platforms and ECC schemes

This patch
 - refactors gpmc_hwecc_bch_capable()
 - add checks for new platforms like dra7xx, am43xx
 - add checks for OMAP3 SoC, w.r.t. new ECC schemes spawned in following commit:
    commit ac65caf5
    ARM: OMAP2+: cleaned-up DT support of various ECC schemes

Signed-off-by: Pekon Gupta <pekon@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>