Add optional MLA (#188)

* Deepseek MLA Optimizations

Co-authored-by: Stanisław Szymczyk <sszymczy@gmail.com>

* Make MLA optional

* Remove some unnecessary copies in the MLA attention

* Deepseek MLA Optimizations V2 (#195)

* Avoid allocating MHA KV cache when MLA is turned on

* Added missing gguf-py file

* Added final optimizations

Co-authored-by: Stanisław Szymczyk <sszymczy@gmail.com>

* Make sure we do have wk_b and wv_b before enabling MLA

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Co-authored-by: Stanisław Szymczyk <sszymczy@gmail.com>
Co-authored-by: Iwan Kawrakow <iwan.kawrakow@gmail.com>

* Use type_k and type_v to set the types of the MLA caches

They were hard-coded at f16.
On my Ryzen-7950X with native bf16 support I get a fairly
significant PP performance boost with bf16 KV-cache:
PP-4096 = 320 t/s up from 292 t/s with fp16 KV-cache.

* Better gemm strategy when nth > nhead

It gives a ~10% PP performance boost for DeepSeek-Lite with 32 threads
(with or without MLA).
Before this commit, when nth > nhead heads were processed
sequentially with all nth threads participating in each
matrix multiplication. Now we ind the gcd of nhead and
nth and split threads into nth/gcd groups, each group
processing nhead/gcd heads.

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Co-authored-by: Saood Karim <saood05@gmail.com>
Co-authored-by: Stanisław Szymczyk <sszymczy@gmail.com>
Co-authored-by: Iwan Kawrakow <iwan.kawrakow@gmail.com>

include/llama.h

@@ -374,6 +374,7 @@ extern "C" {
         bool embeddings;  // if true, extract embeddings (together with logits)
         bool offload_kqv; // whether to offload the KQV ops (including the KV cache) to GPU
         bool flash_attn;  // whether to use flash attention [EXPERIMENTAL]
+        bool mla_attn;    // whether to use MLA attention [EXPERIMENTAL]
 
         // Abort callback
         // if it returns true, execution of llama_decode() will be aborted