one bus mutex for the eeprom read/write issue

[xwang9]

- What I did
one bus mutex for the eeprom read/write issue for fishbone32 and fishbone48
- How I did it
just use one mutex in function fpga_i2c_access

- How to verify it
no "ff ff" and sfp no detected issue.

- Description for the changelog

one bus mutex for the eeprom read/write issue for fishbone32 and fishbone48

- A picture of a cute animal (not mandatory but encouraged)

[xwang9]

performance compare between one bus mutex and multi bus mutex on fishbone48

use old fpga, plug in 48+8 optical module(loopback), do not stop xcvr thread. use cmd "sfputil show eeprom --raw" to do the test. use attached script as background thread.
Seems the performance not so bad on Fishbone48 when use one bus mutex.

#############multi bus mutex:

no background thread
real 0m3.845s
user 0m1.092s
sys 0m2.724s

real 0m3.884s
user 0m1.140s
sys 0m2.712s

####### 1 background thread
real 0m3.880s
user 0m1.144s
sys 0m2.704s

real 0m5.289s
user 0m1.064s
sys 0m3.384s

real 0m5.905s
user 0m1.148s
sys 0m4.072s

######## 2 background thread
real 0m6.848s
user 0m1.052s
sys 0m4.460s

real 0m5.763s
user 0m1.080s
sys 0m3.908s

real 0m4.991s
user 0m1.036s
sys 0m3.420s

####### 3 background thread
real 0m4.820s
user 0m1.004s
sys 0m3.348s

real 0m7.724s
user 0m1.084s
sys 0m4.532s

real 0m10.063s
user 0m1.124s
sys 0m4.748s

######################new driver (use one bus mutex)

no background thread
real 0m3.906s
user 0m1.152s
sys 0m2.732s

real 0m3.912s
user 0m1.140s
sys 0m2.744s

real 0m3.794s
user 0m1.048s
sys 0m2.720

######## 1 background thread
real 0m4.884s
user 0m0.992s
sys 0m3.560s

real 0m6.338s
user 0m1.068s
sys 0m4.216s

real 0m5.006s
user 0m1.116s
sys 0m3.412s

####### 2 background thread
real 0m7.207s
user 0m0.956s
sys 0m4.412s

real 0m7.410s
user 0m1.128s
sys 0m4.232s

real 0m8.267s
user 0m1.196s
sys 0m4.588s

######## 3 background thread
real 0m9.946s
user 0m1.136s
sys 0m4.492s

real 0m10.837s
user 0m0.988s
sys 0m4.584s

real 0m10.701s
user 0m1.044s
sys 0m4.572s

[xwang9]

background thread script:

#!/bin/sh
i=1
while true

do
#echo "--------------- times=${i} -------------" | tee -a ./loopback_test_$1.log
echo "--------------- times=${i} -------------" >> ./loopback_test_$1.log

sfputil show eeprom --raw > log_$1 2>&1
#sfputil show eeprom --raw --port Ethernet1 > log
#i2cdump -y -f 10 0x50 2>&1 > log
sync
cat ./log_$1 >> ./loopback_test_$1.log

#grep "ff ff" ./log_$1
#if [ $? -eq 0 ];then

break

#fi

i=$((${i}+1))
done

[pphuchar]

@xwang9 Please resolve the conflict by click "rebase and merge" on this xwang9#1
This will resolve the conflicts. Then we can merge this PR.