uboot-phytec

net: phy: ti: dp83867: enable reading of ext registers

Enable reading of dp83867 PHY external registers by implementing .readext()
and .writeext() callbacks.

cmd examples:
=>  mdio rx cpsw_nuss@046000000 0 0x1f.0x86
Reading from bus cpsw_nuss@046000000
PHY at address 0:
31.134 - 0x7
=> mdio rx cpsw_nuss@046000000 0 0x1f.0x80-0x86
Reading from bus cpsw_nuss@046000000
PHY at address 0:
31.128 - 0x0
31.129 - 0x0
31.130 - 0x5ad6
31.131 - 0x7ff6
31.132 - 0x0
31.133 - 0x7e
31.134 - 0x7

Note.  It's fixed upstream already (more then two commits), but commands to
be used is:
 => mdio r cpsw_nuss@046000000 0 0x1f.0x80-0x86 - no "x"

Reviewed-by: Dan Murphy <dmurphy@ti.com>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>