MA-14501[Android] Set BOOTAUX_RESERVED_MEM macro to iMX8 defconfig

MA-14501[Android] Set BOOTAUX_RESERVED_MEM macro to iMX8 defconfig

As the M4 use different DDR memory size in normal android/car2 and car
image, use different defconfig for car2 to decrease DDR memory
reservation. So memory reserved for each M4 core is 8MB in car2 and
normal android image. it's 32MB for car image.

Change-Id: Idf608f539cd614a154c78e3a1af28eff1da5c1f2
Signed-off-by: Zhang Bo <bo.zhang@nxp.com>
Signed-off-by: Ye Li <ye.li@nxp.com>
(cherry picked from commit 565f2204e7925d3bd25623ff1104a54ee0f8a601)
(cherry picked from commit fdb033f37174713728132fd8e933225019c3aec5)