ARM: mach-omap2: omap5/dra7: Enable ACTLR[0] (Enable invalidates of BTB) to facilitate CVE_2017-5715 WA in OS

Enable CVE_2017_5715 and since we have our own v7_arch_cp15_set_acr
function to setup the bits, we are able to override the settings.

Without this enabled, Linux kernel reports:
CPU0: Spectre v2: firmware did not set auxiliary control register IBE bit, system vulnerable

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

NOTE: This by itself does not enable the workaround for CPU1 (on
OMAP5 and DRA72/AM572 SoCs) and may require additional kernel patches.
Signed-off-by: NNishanth Menon <nm@ti.com>