sf: Add XMC xm25qh64a and xm25qh128a entries

This patch adds support for 2 new XMC (Wuhan Xinxin Semiconductor
Manufacturing Corp) SPI NOR chips.

This support can be enabled by selecting the SPI_FLASH_XMC Kconfig
option.

Signed-off-by: Stefan Roese <sr@denx.de>
Reviewed-by: Jagan Teki <jagan@openedev.com>