uboot-imx

tegra: fix Makefile to pass per-file CFLAGS

Since Kbuild was introduced, warmboot_avp.o has been compiled
without -march=armv4t.

Makefile should be adjusted to pass a per-file option.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Stephen Warren <swarren@nvidia.com>
Cc: Tom Warren <twarren@nvidia.com>