RISC-V: Add Zvfbfwma extension to the -march= option

RISC-V: Add Zvfbfwma extension to the -march= option

This patch would like to add new sub extension (aka Zvfbfwma) to the
-march= option. It introduces a new data type BF16.

1 In spec: "Zvfbfwma requires the Zvfbfmin extension and the Zfbfmin extension."
  1.1 In Embedded    Processor: Zvfbfwma -> Zvfbfmin -> Zve32f
  1.2 In Application Processor: Zvfbfwma -> Zvfbfmin -> V
  1.3 In both scenarios, there are: Zvfbfwma -> Zfbfmin

2 Zvfbfmin's information is in:
<https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=1ddf65c5fc6ba7cf5826e1c02c569c923a541c09>

3 Zfbfmin's formation is in:
<https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=35224ead63732a3550ba4b1332c06e9dc7999c31>

4 Depending on different usage scenarios, the Zvfbfwma extension may
depend on 'V' or 'Zve32f'. This patch only implements dependencies in
scenario of Embedded Processor. This is consistent with the processing
strategy in Zvfbfmin. In scenario of Application Processor, it is
necessary to explicitly indicate the dependent 'V' extension.

5 You can locate more information about Zvfbfwma from below spec doc:
<https://github.com/riscv/riscv-bfloat16/releases/download/v59042fc71c31a9bcb2f1957621c960ed36fac401/riscv-bfloat16.pdf>

gcc/ChangeLog:

	* common/config/riscv/riscv-common.cc:
	(riscv_implied_info): Add zvfbfwma item.
	(riscv_ext_version_table): Ditto.
	(riscv_ext_flag_table): Ditto.
	* config/riscv/riscv.opt:
	(MASK_ZVFBFWMA): New macro.
	(TARGET_ZVFBFWMA): Ditto.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/arch-37.c: New test.
	* gcc.target/riscv/arch-38.c: New test.
	* gcc.target/riscv/predef-36.c: New test.
	* gcc.target/riscv/predef-37.c: New test.