phycore_imx8mp: Rework some of the RAM related Kconfig symbols

As the code is today, we get a warning about "select" statements on
"choice" options not doing anything. In this case we can easily fix this
by dropping the select line as the following choice statement handles
things correctly. We also drop the "default false" line as false / n is
the default.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Teresa Remmet <t.remmet@phytec.de>
diff --git a/board/phytec/phycore_imx8mp/Kconfig b/board/phytec/phycore_imx8mp/Kconfig
index bdf9e97..caf9cb0 100644
--- a/board/phytec/phycore_imx8mp/Kconfig
+++ b/board/phytec/phycore_imx8mp/Kconfig
@@ -45,7 +45,6 @@
 
 config PHYCORE_IMX8MP_RAM_SIZE_8GB
 	bool "8GB RAM"
-	select PHYCORE_IMX8MP_USE_2GHZ_RAM_TIMINGS
 	help
 	  Set RAM size fix to 8GB for phyCORE-i.MX8MP.
 	  Only 2GHz RAMs are supported.
@@ -54,7 +53,6 @@
 
 config PHYCORE_IMX8MP_RAM_FREQ_FIX
 	bool "Set phyCORE-i.MX8MP RAM frequency fix instead of detecting"
-	default false
 	help
 	  RAM frequency is automatic being detected with the help of
 	  the EEPROM introspection data. Set RAM frequency to a fix value