gdb/riscv: Remove riscv_type_alignment function

gdb/riscv: Remove riscv_type_alignment function

Make use of the type_align function and remove riscv_type_alignment as
it is no longer needed.  I tested this against a number of RV32 and
RV64 targets, and I also ran the tests with an assertion in place
checking that the old riscv_type_alignment function gives the same
answer as the common type_align function - it does, and all the tests
still pass.

gdb/ChangeLog:

	* riscv-tdep.c (riscv_type_align): New function.
	(riscv_type_alignment): Delete.
	(riscv_arg_location): Use 'type_align'.
	(riscv_gdbarch_init): Register riscv_type_align gdbarch function.