wifi: rtlwifi: add calculate_bit_shift()

wifi: rtlwifi: add calculate_bit_shift()

There are many same functions like _rtl88e_phy_calculate_bit_shift(),
_rtl92c_phy_calculate_bit_shift() and so on. And these functions can
cause undefined bitwise shift behavior. Add calculate_bit_shift() to
replace them and fix undefined behavior in subsequent patches.

Signed-off-by: Su Hui <suhui@nfschina.com>
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/20231219065739.1895666-2-suhui@nfschina.com