ARM: OMAP4: Fix compiler warning

Latest gcc 6.2 compiler is throwing the below warning for omap4_panda_defconfig
arch/arm/mach-omap2/omap4/hw_data.c:136:3: warning: 'abe_dpll_params_sysclk_196608khz' defined but not used [-Wunused-const-variable=]
   abe_dpll_params_sysclk_196608khz[NUM_SYS_CLKS] = {

Fix this by guarding it with CONFIG_SYS_OMAP_ABE_SYSCK

Reported-by: Dan Murphy <dmurphy@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>