designware_i2c: remove inclusion of <asm/arch/hardware.h>

As soon as all boards have their CONFIG_SYS_I2C_BASE defined in
configuration files instead of "asm/arch/hardware.h" it's safe to remove
the inclusion in question and make driver platform-independent.

Cc: Tom Rini <trini@ti.com>
Cc: Heiko Schocher <hs@denx.de>
Cc: Stefan Roese <sr@denx.de>
Cc: Vipin Kumar <vipin.kumar@st.com>
Cc: Armando Visconti <armando.visconti@st.com>

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>