ARM: OMAP2420: Fix ethernet support for OMAP2420 H4

Ethernet is not currently working on the OMAP2420 H4 board. In commit
f6049312 (ARM: OMAP: abstract debug card setup (smc, leds)) the function
h4_init_smc91x() that initialised the ethernet controller was renamed to
h4_init_debug() but was never called when initialising the board.

Adding a call to h4_init_debug() fixes ethernet support, however,
instead of using the legacy H4 code migrate the H4 to use the
gpmc_smc91x_init() function instead and remove the legacy H4 code.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>