Handle Alpha load-immediate-FP pseudo-instructions:

Handle Alpha load-immediate-FP pseudo-instructions:
* config/alpha-opcode.h (ldif, ldig, ldis, ldit): New patterns.
* config/tc-alpha.c (lit8_sec, lit4_sec, lit8_sym, lit4_sym): New variables.
(create_literal_section): New function.
(create_lita_section): Now a macro.
(get_lit8_offset, get_lit4_offset): New functions.
(maybe_set_gp): New function.
(select_gp_value): Call it.
(load_expression): Preserve addend if symbol is a section symbol.
(alpha_ip): Handle new operand type `F' for floating-point constants; store
them in .lit{4,8} sections.
(alpha_ip, case 'G'): Emit LITUSE relocations for symbol exprs.