microblaze: branch to base vector address on reset

Current code assumes that the vector base address is always at 0x0.
However, this value is configurable for MicroBlaze using the
CONFIG_XILINX_MICROBLAZE0_VECTOR_BASE_ADDR Kconfig option. Update the
reset routines to branch to this location instead.

Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Link: https://lore.kernel.org/r/20211130163358.2531677-10-ovidiu.panait@windriver.com


Signed-off-by: Michal Simek <michal.simek@xilinx.com>