LoongArch: Add support code model extreme.

LoongArch: Add support code model extreme.

Use five instructions to calculate a signed 64-bit offset relative to the pc.

gcc/ChangeLog:

	* config/loongarch/loongarch-opts.cc: Allow cmodel to be extreme.
	* config/loongarch/loongarch.cc (loongarch_call_tls_get_addr):
	Add extreme support for TLS GD and LD types.
	(loongarch_legitimize_tls_address): Add extreme support for TLS LE
	and IE.
	(loongarch_split_symbol): When compiling with -mcmodel=extreme,
	the symbol address will be obtained through five instructions.
	(loongarch_print_operand_reloc): Add support.
	(loongarch_print_operand): Add support.
	(loongarch_print_operand_address): Add support.
	(loongarch_option_override_internal): Set '-mcmodel=extreme' option
	incompatible with '-mno-explicit-relocs'.
	* config/loongarch/loongarch.md (@lui_l_hi20<mode>):
	Loads bits 12-31 of data into registers.
	(lui_h_lo20): Load bits 32-51 of the data and spell bits 0-31 of
	the source register.
	(lui_h_hi12): Load bits 52-63 of the data and spell bits 0-51 of
	the source register.
	* config/loongarch/predicates.md: Symbols need to be decomposed
	when defining the macro TARGET_CMODEL_EXTREME
	* doc/invoke.texi: Modify the description information of cmodel in the document.
	Document -W[no-]extreme-plt.

gcc/testsuite/ChangeLog:

	* gcc.target/loongarch/func-call-1.c: Add option '-mcmodel=normal'.
	* gcc.target/loongarch/func-call-2.c: Likewise.
	* gcc.target/loongarch/func-call-3.c: Likewise.
	* gcc.target/loongarch/func-call-4.c: Likewise.
	* gcc.target/loongarch/func-call-5.c: Likewise.
	* gcc.target/loongarch/func-call-6.c: Likewise.
	* gcc.target/loongarch/func-call-7.c: Likewise.
	* gcc.target/loongarch/func-call-8.c: Likewise.
	* gcc.target/loongarch/relocs-symbol-noaddend.c: Likewise.
	* gcc.target/loongarch/func-call-extreme-1.c: New test.
	* gcc.target/loongarch/func-call-extreme-2.c: New test.