pinctrl: uniphier: rename macros for drive strength control

The new ARMv8 SoC, PH1-LD20, supports more fine-grained drive
strength control.  Some of the configuration registers on it have
3-bit width.

The feature will be supported in the next commit, but a problem is
that macro names are getting longer and longer in the current naming
scheme.

Before moving forward, this commit renames macros as follows:

  UNIPHIER_PIN_DRV_4_8        -> UNIPHIER_PIN_DRV_1BIT
  UNIPHIER_PIN_DRV_8_12_16_20 -> UNIPHIER_PIN_DRV_2BIT
  UNIPHIER_PIN_DRV_FIXED_4    -> UNIPHIER_PIN_DRV_FIXED4
  UNIPHIER_PIN_DRV_FIXED_5    -> UNIPHIER_PIN_DRV_FIXED5
  UNIPHIER_PIN_DRV_FIXED_8    -> UNIPHIER_PIN_DRV_FIXED8

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>