target/xtensa: add geometry to xtensa_get_regfile_by_name

target/xtensa: add geometry to xtensa_get_regfile_by_name

Register file name may not uniquely identify a register file in the set
of configurations. E.g. floating point registers may have different size
in different configurations. Use register file geometry as additional
identifier.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>