microblaze: add Kconfig symbol for the vector base address

MicroBlaze vector base address is configurable (hdl C_BASE_VECTORS
configuration parameter). Current code assumes that the reset vector
location is always 0x0.

Add the XILINX_MICROBLAZE0_VECTOR_BASE_ADDR Kconfig option so the user
can adjust the reset vector address.

Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Link: https://lore.kernel.org/r/20211130163358.2531677-8-ovidiu.panait@windriver.com


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