I enabled early printk and found that kernel actually stuck here..
Normal Boot
Hit any key to stop autoboot: 0
reading m4_pzt_application.bin
29628 bytes read in 18 ms (1.6 MiB/s)
## Starting auxiliary core at 0x007F8000 ...
switch to partitions #0, OK
mmc2(part 0) is current device
switch to partitions #0, OK
mmc2(part 0) is current device
reading boot.scr
** Unable to read file boot.scr **
reading zImage
5582152 bytes read in 158 ms (33.7 MiB/s)
Booting from mmc ...
reading imx6sx-sdb-m4.dtb
38359 bytes read in 18 ms (2 MiB/s)
Kernel image @ 0x80800000 [ 0x000000 - 0x552d48 ]
## Flattened Device Tree blob at 83000000
Booting using the fdt blob at 0x83000000
Using Device Tree in place at 83000000, end 8300c5d6
switch to ldo_bypass mode!
## else Transferring control to Linux (at address 80800000)...
DEBUG: =====Starting kernel ...
DEBUG: Before bootstage_mark_name
DEBUG: after bootstage_mark_name
DEBUG: Before cleanup_before_linux
DEBUG: After cleanup_before_linux
==DEBUG: Before kernel_entry
Uncompressing Linux... done, booting the kernel.