arch/x86: Remove most C_ENV_BOOTBLOCK_SIZE limits

With top-aligned bootblock this is no longer globally needed.
The default maximum is now a generous 256 KiB with couple
platforms having lower limits of 32 KiB and 64 KiB.

Change-Id: Ib1aee44908c0dcbc17978d3ee53bd05a6200410c
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/47600
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/arch/x86/Kconfig

@@ -186,10 +186,13 @@ config HPET_ADDRESS
 	hex
 	default 0xfed00000 if !HPET_ADDRESS_OVERRIDE
 
-# 64KiB default bootblock size
 config C_ENV_BOOTBLOCK_SIZE
 	hex
-	default 0x10000
+	default 0x40000 if !FIXED_BOOTBLOCK_SIZE
+	help
+	   This is only the default maximum of bootblock size for linking
+	   purposes. Platforms may provide different limit and need to
+	   specify this when FIXED_BOOTBLOCK_SIZE is selected.
 
 config FIXED_BOOTBLOCK_SIZE
 	bool