clk: mediatek: Add configurable enable control to mtk_pll_data

clk: mediatek: Add configurable enable control to mtk_pll_data

In all MediaTek PLL design, bit0 of CON0 register is always
the enable bit.
However, there's a special case of usbpll on MT8192.
The enable bit of usbpll is moved to bit2 of other register.
Add configurable en_reg and pll_en_bit for enable control or
default 0 where pll data are static variables.
Hence, CON0_BASE_EN could also be removed.
And there might have another special case on other chips,
the enable bit is still on CON0 register but not at bit0.

Reviewed-by: Ikjoon Jang <ikjn@chromium.org>
Signed-off-by: Weiyi Lu <weiyi.lu@mediatek.com>
Signed-off-by: Chun-Jie Chen <chun-jie.chen@mediatek.com>
Link: https://lore.kernel.org/r/20210726105719.15793-8-chun-jie.chen@mediatek.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>