regulator: msm_gfx_ldo: Update the fusing scheme for GFX LDO

Change the LDO_EN bit definition for GFX LDO on MSM8953 and
remove the LDO bypass fusing logic as it is not supported.

While at it, add the debugfs node to disable ldo_mode.
Disable LDO mode: echo 1 > /d/msm_gfx_ldo/ldo_mode_disable
Enable  LDO mode: echo 0 > /d/msm_gfx_ldo/ldo_mode_disable

CRs-Fixed: 989270
Change-Id: Ibc7aa921380e89da4963571408b89bc417dec245
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>