arm64: Enable ARCH_HAS_RESET_CONTROLLER for ARCH_BRCMSTB

Allow the use of reset controllers on ARCH_BRCMSTB such as the recently
introduced RESET_BRCMSTB driver.

Signed-off-by: Jim Quinlan <jim2101024@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>