mpt2sas: Added phy_enable and set_phy_speed sysfs callback support.

Added new callbacks phy_enable and set_phy_speed in the mpt2sas_transport_functions template. This will allow end user to enable/disable phys and change links rates using the SysFS interface. Current implementation only supports direct attached phys, but we could in the future add support for expander based phys.
A new subroutine mpt2sas_config_set_sas_iounit_pg1 was added; this wrapper function used to send request to controller firmware to modify the phys and link rates. A new subroutine _transport_find_local_phy was added; a function for easly obtaining the local phy object for direct attached.

Example to disable a phy
echo 0 > /sys/class/phy3:0/enable

Example to enable the same phy
echo 1 > /sys/class/phy3:0/enable

Example to change the link rate to 1.5
#echo "1.5 Gbit" > /sys/class/phy3:0/maximum_linkrate #cat /sys/class/phy3:0/negotiated_linkrate 1.5 Gbit

Example to change the link rate to 3.0
#echo "3.0 Gbit" > /sys/class/phy3:0/maximum_linkrate #cat /sys/class/phy3:0/negotiated_linkrate 3.0 Gbit

Example to change the link rate to 6.0
#echo "6.0 Gbit" > /sys/class/phy3:0/maximum_linkrate #cat /sys/class/phy3:0/negotiated_linkrate 6.0 Gbit

---

index 014318f..93c067f 100644
@@ -853,6 +853,8 @@ int mpt2sas_config_set_iounit_pg1(struct MPT2SAS_ADAPTER *ioc, Mpi2ConfigReply_t
     *mpi_reply, Mpi2IOUnitPage1_t *config_page);
 int mpt2sas_config_get_sas_iounit_pg1(struct MPT2SAS_ADAPTER *ioc, Mpi2ConfigReply_t
     *mpi_reply, Mpi2SasIOUnitPage1_t *config_page, u16 sz);
+int mpt2sas_config_set_sas_iounit_pg1(struct MPT2SAS_ADAPTER *ioc,
+    Mpi2ConfigReply_t *mpi_reply, Mpi2SasIOUnitPage1_t *config_page, u16 sz);
 int mpt2sas_config_get_ioc_pg8(struct MPT2SAS_ADAPTER *ioc, Mpi2ConfigReply_t
     *mpi_reply, Mpi2IOCPage8_t *config_page);
 int mpt2sas_config_get_expander_pg0(struct MPT2SAS_ADAPTER *ioc, Mpi2ConfigReply_t