tegra: mark BPMP driver as little-endian only

The BPMP firmware driver never worked on big-endian kernels, and
cannot easily be made portable. Add a dependency to make this clear
in case anyone ever wants to try a big-endian kernel on this hardware.

Link: https://lore.kernel.org/linux-arm-kernel/Y34FCQ3xTmcjqKRT@orome/
Signed-off-by: Arnd Bergmann <[e-mail]>

drivers/firmware/tegra/Kconfig

···
 config TEGRA_BPMP
 	bool "Tegra BPMP driver"
 	depends on ARCH_TEGRA && TEGRA_HSP_MBOX && TEGRA_IVC
+	depends on !CPU_BIG_ENDIAN
 	help
 	  BPMP (Boot and Power Management Processor) is designed to off-loading
 	  the PM functions which include clock/DVFS/thermal/power from the CPU.