ARM: mach-omap2: omap3/am335x: Enable ACR::IBE on Cortex-A8 SoCs for CVE-2017-5715

Enable CVE-2017-5715 option to set the IBE bit. This enables kernel
workarounds necessary for the said CVE.

With this enabled, Linux reports:
CPU0: Spectre v2: using BPIALL workaround

This workaround may need to be re-applied in OS environment around low
power transition resume states where context of ACR would be lost (off-mode
etc).

Signed-off-by: Nishanth Menon <nm@ti.com>