rockchip: make_fit_atf: use elf entry point

rockchip: make_fit_atf: use elf entry point

make_fit_atf.py uses physical address of first segment as the
entry point to bl31. It is incorrect and causes following abort
when bl31_entry() is called:

U-Boot SPL board initTrying to boot from MMC1
"Synchronous Abort" handler, esr 0x02000000
elr: 0000000000000000 lr : 00000000ff8c7e8c
x 0: 00000000ff8e0000 x 1: 0000000000000000
x 2: 0000000000000000 x 3: 00000000ff8e0180
x 4: 0000000000000000 x 5: 0000000000000000
x 6: 0000000000000030 x 7: 00000000ff8e0188
x 8: 00000000000001e0 x 9: 0000000000000000
x10: 000000000007fcdc x11: 00000000002881b8
x12: 00000000000001a2 x13: 0000000000000198
x14: 000000000007fdcc x15: 00000000002881b8
x16: 00000000003c0724 x17: 00000000003c0718
x18: 000000000007fe80 x19: 00000000ff8e0000
x20: 0000000000200000 x21: 00000000ff8e0000
x22: 0000000000000000 x23: 000000000007fe30
x24: 00000000ff8d1c3c x25: 00000000ff8d5000
x26: 00000000deadbeef x27: 00000000000004a0
x28: 000000000000009c x29: 000000000007fd90

Fix it by using the entry point from the elf header.

Signed-off-by: Mian Yousaf Kaukab <yousaf.kaukab@suse.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>