RISC-V: Accept constant operands in la and lla

opcodes/
	PR gas/23305
	* riscv-opc.c (riscv_opcodes): Use new format specifier 'B' for
	la and lla.

gas/
	PR gas/23305
	* config/tc-riscv.c (riscv_ip): Add format specifier 'B' for
	constants and symbols.
	* testsuite/gas/riscv/lla32.d: New file.
	* testsuite/gas/riscv/lla32.s: Likewise.
	* testsuite/gas/riscv/lla64-fail.d: Likewise.
	* testsuite/gas/riscv/lla64-fail.l: Likewise.
	* testsuite/gas/riscv/lla64-fail.s: Likewise.
	* testsuite/gas/riscv/lla64.d: Likewise.
	* testsuite/gas/riscv/lla64.s: Likewise.