phy: msm: qusb: Support reading of efuse value from two regs

Add support for reading HSTX_TRIM value from two registers
(tune2_efuse_reg and tune2_efuse_reg + 4) to write to
QUSB2PHY_PORT_TUNE2 register for better eye-diagram.
While at it, also refactor the code to remove unnecessary
checks/initializations. Also add missing Documentation.

Change-Id: Ifda2dfe90c35f24cfd55c6ab369301c5bf40e11e
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>