OpenBLT XMC1400 with larger bootloader file

I found out that I needed to add the below lines to the startup_XMC1400.S file before the section that initializes the interrupt vector.

ldr r0, =__initial_sp
mov sp, r0

It fixes an issue with the stack pointer. If anyone ports OpenBLT to a board and finds that thier application is getting stuck in an infinite loop when the bootloader jumps to the application, the above lines may fix the issue.