cpu: rv64: matmul: add dropout attribute check

[zhangfeiv0]

Description

This issue was introduced by #3784, and the error occurs as follows:

./tests/benchdnn/benchdnn --matmul --stag=ab --dtag=ab --attr-dropout=0.5:12345678 1x1:1x1
Error: Function 'initialize_memory_create' at (/data/zhangfei/oneDNN/tests/benchdnn/dnnl_memory.cpp:880) returned 'invalid_arguments'
[CHECK_MEM][ERROR]: Allocations were not cleared
[CHECK_MEM][ERROR]: Total size wasn't reduced to 0

Therefore, add a check for the dropout attribute to fall back to the generic implementation and avoid the error. The effect of applying this PR is as follows:

./tests/benchdnn/benchdnn --matmul --stag=ab --dtag=ab --attr-dropout=0.5:12345678 1x1:1x1
0:PASSED (13 ms) __REPRO: --matmul --stag=ab --dtag=ab --attr-dropout=0.5:12345678 1x1:1x1
============================================================
= Implementation statistics (--summary=no-impl to disable) =
============================================================
| ref:any : 1 (100%)                                       |
============================================================
tests:1 passed:1 skipped:0 mistrusted:0 unimplemented:0 invalid_arguments:0 failed:0 listed:0
total: 0.01s; create_pd: 0.00s (2%); create_prim: 0.00s (0%); fill: 0.00s (6%); execute: 0.00s (0%); compute_ref: 0.00s (0%); compare: 0.01s (78%);