arm: Adjust entry point of XIP kernels to the __reset function

The entry point specified in the elf file should always point to
executable code, and not to the interrupt vector table.  Pointing to the
vector table as the entry point in the elf file presents problems with
running the kernel against a debugger as the debugger starts the program
counter at the top of the interrupt vector table.

Change-Id: I76051f6e99a44bab72936670bead5fb8191a6ec7
Signed-off-by: Tim Nordell <tim.nordell@nimbelink.com>