cc: Improve -mcpu target for kryo385 (SDM845)

Google added the kryo385 variant for SDM845 on Pixel 3/XL because
kryo385 does not have the dot product extension required in
cortex-a75/a55 variants [1]. Google resorted to cortex-a53 as
a conservative option for kryo385, but cortex-a53 is ARMV8A instead
of ARMV8_2A, and it lacks a couple of features like fp16 and rcpc
compared to cortex-a55/a75, according to LLVM's
AArch64TargetParser.def [2].

Since the only concern of using cortex-a55 for kryo385 is the dot
product extension, disable dotprod by passing +nodotprod to -mcpu.
This type of flag has been supported by LLVM since 2015 [3].

Test: build with kryo385 as the cpu variant and boot

[1] https://android-review.googlesource.com/c/platform/build/soong/+/831260
[2] https://github.com/llvm/llvm-project/blob/main/llvm/include/llvm/Support/AArch64TargetParser.def
[3] https://github.com/llvm/llvm-project/commit/7b0a7d8d1e35720e55805587cadf7973bba36032



Signed-off-by: Chenyang Zhong <zhongcy95@gmail.com>
Change-Id: Ide8e5be07d54f65aa2ce677bd5b6b8d04509ee39