refactor(plat/nxp/common): moved plat make-variables to new plat_common_def.mk

Move some common make variables to new plat_common_def.mk,
then it can be reused by other platforms.

Signed-off-by: Jiafei Pan <Jiafei.Pan@nxp.com>
Change-Id: I37bd65b0f8124f63074fa03339f886c2cdb30bd3
1 file changed